| Processing Steps |
- Parameter or Variable: SEA GRASSES - CANOPY HEIGHT (measured); Units: centimeter; Observation Category: in situ; Sampling Instrument: meterstick; Sampling and Analyzing Method: The four corners of the boat (port-stern, port-bow, starboard-bow, and starboard-stern) were used as seagrass sample locations. Measurements were taken approximately 2-4 meters from the boat by tossing a 0.25 m2 quadrat into the water and using a meter stick. Within each quadrat, five random shoots were extracted for canopy height measurements for each seagrass species present. Blade lengths were determined as the photosynthetic portion of the longest blade from each shoot.; Data Quality Method: The data were carefully reviewed by all authors..
- Parameter or Variable: WIND GUST (calculated); Units: kilometers per hour; Observation Category: model output; Sampling Instrument: ArcGIS for Desktop; Sampling and Analyzing Method: We used 10-m maximum sustained wind gusts obtained from 70 weather locations reported by the National Weather Service (NWS; M. Buchanan) in the NOAA National Hurricane Center Hurricane Harvey tropical cyclone report (Blake and Zelinsky 2018). In ArcMap 10.3 (Environmental Systems Research Institute), we imported these wind data and used Inverse-Distance Weighting (IDW) interpolation to assign values to areas between sampling points, weighted by distance. We used 12 sampling stations identified from a variable search radius (100 m2) to generate a predicted value for each unknown point. We then used the tool ‘Extract Values to Points’ to extract cell values of the interpolated wind raster for each of the 525 seagrass sampling stations.; Data Quality Method: The data were carefully reviewed by all authors..
- Parameter or Variable: SEDIMENTS - DRY WEIGHT (measured); Units: gram; Observation Category: laboratory analysis; Sampling Instrument: sediment sieve; Sampling and Analyzing Method: To determine sediment grain size, sand/silt/clay ratios were determined following the methods of Folk (1964). Percent contribution by weight was measured for four components: rubble (shell), sand, silt, and clay. A 20-ml sediment sample was mixed with 100 ml of 3% hydrogen peroxide and 75 ml of de-ionized water to digest organic material in the sample. The sample was then wet sieved through a 63μm mesh stainless steel screen using a vacuum pump and a Millipore Hydrosol SST filter holder to separate rubble and sand from silt and clay. After drying, the rubble (shell) and sand was separated on a 250μm screen. The silt and clay fractions were measured using pipette analysis. Briefly, the settling velocity was used to classify the particles and to determine the percent composition of each fraction, based on weight.; Data Quality Method: The data were carefully reviewed by all authors..
- Parameter or Variable: SEDIMENTS - PARTICLE SIZE FRACTIONS (measured); Units: percent; Observation Category: laboratory analysis; Sampling Instrument: sediment sieve; Sampling and Analyzing Method: To determine sediment grain size, sand/silt/clay ratios were determined following the methods of Folk (1964). Percent contribution by weight was measured for four components: rubble (shell), sand, silt, and clay. A 20-ml sediment sample was mixed with 100 ml of 3% hydrogen peroxide and 75 ml of de-ionized water to digest organic material in the sample. The sample was then wet sieved through a 63μm mesh stainless steel screen using a vacuum pump and a Millipore Hydrosol SST filter holder to separate rubble and sand from silt and clay. After drying, the rubble (shell) and sand was separated on a 250μm screen. The silt and clay fractions were measured using pipette analysis. Briefly, the settling velocity was used to classify the particles and to determine the percent composition of each fraction, based on weight.; Data Quality Method: The data were carefully reviewed by all authors..
- Parameter or Variable: SEA GRASSES - PERCENT COVER (measured); Units: percent; Observation Category: in situ; Sampling Instrument: visual observation; Sampling and Analyzing Method: Species composition and areal coverage were obtained from four replicate quadrat samples per station at each of the four cardinal locations from the vessel boat (port-stern, port-bow, starboard-bow, and starboard-stern). Percent cover of areal biomass was estimated by direct observation, looking down at the seagrass canopy through the water using a 0.25 m2 quadrat framer subdivided into 100 cells.; Data Quality Method: The data were carefully reviewed by all authors..
- Parameter or Variable: AMMONIUM (NH4) (measured); Units: micromole; Observation Category: laboratory analysis; Sampling Instrument: spectrophotometer; Sampling and Analyzing Method: To determine sediment porewater ammonium, thawed then centrifuged the sediment core and processed the supernatant using the colorimetric techniques in Parsons et al. (1984). Once sediment samples were thawed, samples were homogenized by stirring with glass rod or squeezing the bag several times. We weighed each sample + centrifuge tube to the nearest 0.1 g and capped each centrifuge tube immediately after weighing to prevent evaporation from the sediment sample. To obtain the sediment porewater, we set the centrifuge to run for 10-20 min (depending on soil moisture) at 10,000 rpm. We used the following reagents: Ultra pure water; Phenol alcohol: dissolved 5 g reagent-grade phenol in 50 ml 95% ethanol; Sodium nitroprusside solution: dissolved 0.5 g sodium nitroprusside in 100 ml ultra pure water; Alkaline solution: dissolved 80 g sodium citrate and 4.0 g NaOH in 400 ml ultra pure water; Sodium hypochlorite: used commercially available hypochlorite (e.g. Ultra Clorox); Oxidizing solution: mixed 5 ml alkaline solution with 1.25 ml of sodium hypochlorite. For the Standard Curve, we added 133.7 mg NH4Cl (FW = 53.49 g mole-1) to a volumetric flask and bring to 500 ml with ultra pure water (= 5 mM). We then added 1 ml of this solution to a volumetric flask and brought to 100 ml with ultra pure water (= 50 μM). Standard curve and reagents were calculated for 2.5 ml samples. We ran at least three replicates (n = 3) for each concentration. μM concentrations were calculated from μg NH4 +/2.5 ml by multiplying by 22.2 (i.e., (1 μg NH4 +/2.5 ml) x (1000 ml/L) x (1 μmole NH4 +/18 μg NH4 +) = 22.2 μmole/L). To process the samples, we added 2.5 mL of water sample or standard to corresponding test tube. We diluted as necessary with low-ammonia seawater (i.e., “blue water”). For example, for sediments, we diluted 0.5 ml sample with 2.0 ml “blue water”. We added 0.1 ml phenol alcohol to the samples, vortexed, and waited one minute. We then added 0.1 ml sodium nitroprusside solution, vortexed, and waited one minute. Next, we added 0.25 ml oxidizing solution, vortexed, and waited one minute. We mixed samples thoroughly, capped or covered the tube with parafilm and allowed the sample to develop for 1 hr in the dark and at room temperature. On the spectrophotometer, we recorded absorbance at 640 nm and ensured to auto zero the spectrophotometer to blue water blanks that had chemicals added to them. We read standards first and again every 10 samples to ensure spectrophotometer was running properly. We regressed samples absorbance to standard curve considering the dilution factor.; Data Quality Method: The data were carefully reviewed by all authors..
- Parameter or Variable: SEDIMENTS - ORGANIC CARBON (measured); Units: percent; Observation Category: laboratory analysis; Sampling Instrument: scale; Sampling and Analyzing Method: To determine sediment total organic carbon, samples were homogenized, placed in aluminum weighing tins and dried in a 60 ºC oven (to remove water) for 12-24 hr. Samples were then removed from the oven and placed in a desiccator (to prevent moisture from the air changing the sample weight) to cool to room temperature. Once cooled, samples were weighed to the nearest 0.1 g, and placed in a muffle furnace to combust organic material, at 550 ºC for 4 hr. After cooling samples to room temperature in a desiccator, the samples were reweighed and Loss on Ignition (LOI) was calculated using the following formula, where DW is sample dry weight (in grams): LOI550 (as a percentage) = ((DW60 - DW550) / DW60) x 100. The weight loss is proportional to the amount of organic carbon contained in the sample.; Data Quality Method: The data were carefully reviewed by all authors..
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