Data Set (knb-lter-sbc.23.11)

SBC LTER: Beach: Wrack and porewater in southern Santa Barbara County, 2003

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

Protocols and/or Procedures

SBC LTER Intertidal Pore Water Protocols

To investigate relationships between the composition, biomass and cover of macrophyte wrack and the concentrations of dissolved nutrients in intertidal pore water and shallow surf zone water on SBC sandy beaches we sampled 10 beaches during low tides over 1 week in the late summer of 2003, ~5 months after the last rainfall event. Although no information on groundwater was collected or available, the direct influence of terrestrial freshwater runoff and groundwater on intertidal pore water was generally expected to be reduced at this time of year in the study area. Beaches in the study region generally reach peak seasonal sand accumulation and volumes by late summer (Revell et al. 2011). On each beach, we established three shore-normal transects extending from the landward boundary of the beach (the lowest edge of terrestrial vegetation or the base of the sea bluff) to the swash level. Distances between transects were randomly selected. When possible, we sampled an area of the beach with a natural landward boundary and measurable dry sand zone above the high tide strand or drift line.

We estimated the cover, depth, composition and standing stock of macrophyte wrack on each of the three transects (see above) using a line intercept method. The taxa or species, cover (as length) and maximum depth of all drift macrophytes of 0.01 m or more in width that intersected the transect line were measured. The total width of wrack encountered was summed for each transect and a mean of wrack cover was calculated for each beach. The biomass of wrack was measured on each transect by collecting, categorizing and weighing all wrack within in a 1 m wide belt transect that extended from the landward limit of the beach to the high swash limit. Wrack was shaken to remove sand and wet weights of each wrack type or species were measured with a spring balance to the nearest 10 g in the field. Wrack cover and biomass were expressed per meter of the shoreline (meters m-1) to describe a vertical meter-wide strip of intertidal from the high to the low tide zone. This approach is suggested for measurements of biomass, cover and other parameters in sandy beach ecosystems by McLachlan and Brown (2006) to enable comparisons among beaches with different intertidal widths, as sampled in this study, and among different tide, wave and profile conditions at an individual beach.

Pore water samples were generally collected from 3 intertidal levels (high tide strand or drift line (HTS), mid-beach (Mid), and high swash level (HSL) on each of the 3 transects sampled for macrophyte wrack. At each level, a pit was excavated with a spade to a depth where water filled the bottom of the excavation. Interstitial water samples of 50 ml were collected with a plastic syringe from the surface water of each excavation then immediately filtered (Whatman GF/F) into clean 20 ml scintillation vials. It should be noted that water samples were not collected in an oxygen-free environment which may have caused the underestimation of phosphate concentrations. Water samples were also collected in the shallow surf zone immediately seaward of each transect and filtered as above. Water samples were transported to the laboratory on ice and stored frozen until analysis. Salinity of pore water and surf zone water (+/-1) samples was measured with a temperature-compensated refractometer (American Optical).

Concentrations of ammonium-N, nitrate-N, nitrite-N and phosphate-P in pore water and surf zone water samples were determined by flow-injection analysis (FIA-Johnson et al. 1985) at the University of California, Santa Barbara Marine Science Institute Analytical Laboratory. Nitrite concentrations, typically less than 1.0 micromolar, were combined with nitrate (hereafter 'NO2+NO3'). Dissolved organic nitrogen was analyzed by a persulfate digestion method (Doyle et al. 2004).