| Processing Steps |
- Parameter or Variable: water depth (measured); Units: meter; Observation Category: in situ; Sampling Instrument: PVC marked in 10 cm segments; Sampling and Analyzing Method: Station is approached slowly to ensure that the deceleration of the boat does not create a wake and resuspend sediments into the water column. All hydrographic and water column measurements are collected while the vessel is set to drift over the station to minimize interference from sediment plumes generated from physical disturbances of the bottom. Sonde deployment, water transparency and water sample collection must occur within 30 m of the station location. Measurements are made in the following order: (1) PAR, (2) visibility, (3) hydrography, (4) TSS, (5) depth, (6) percent coverage, (7) canopy height, and (8) blade samples for C:N:P ratios. While taking measurements, care is taken not to disturb the sediment or agitate seagrasses. Depth is measured using a PVC pipe marked in 10 cm segments. Care is taken to avoid allowing the PVC pole to sink into soft sediments.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: DISSOLVED OXYGEN (measured); Units: milligram/liter; Observation Category: in situ; Sampling Instrument: YSI - handheld multi-parameter instrument; Sampling and Analyzing Method: Station is approached slowly to ensure that the deceleration of the boat does not create a wake and resuspend sediments into the water column. All hydrographic and water column measurements are collected while the vessel is set to drift over the station to minimize interference from sediment plumes generated from physical disturbances of the bottom. Sonde deployment, water transparency and water sample collection must occur within 5 m of the station location. Measurements are made in the following order: (1) PAR, (2) visibility, (3) hydrography, (4) water samples, (5) depth, (6) biomass cores. While taking measurements, care is taken not to disturb the sediment or agitate seagrasses. The sonde is lowered so that the instrument probes are completely submerged.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: bottom irradiance (calculated); Units: micromole photons/m2/sec; Observation Category: in situ; Sampling Instrument: PAR Sensor; Sampling and Analyzing Method: Near-continuous underwater measurements of canopy-level photosynthetically active radiation (PAR = ca. 400 to 700 nm wavelength) began at LM-151 in 1989 using a LI-193SA spherical (4π) quantum sensor connected to a LI-1000 datalogger (LI-COR Inc., Lincoln, Nebraska, USA). Measurements were taken every minute and integrated over the hour before logging. Average daytime irradiance (ADI) was calculated by taking the monthly mean of daily averaged irradiance values between sunrise and sunset. This metric was chosen for analysis to minimize daily light variability and reflect growing conditions. A thin, optically-clear plastic covering was placed over the sensor and replaced ever 2 - 4 wk to reduce biofouling.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: pH (measured); Units: pH; Observation Category: in situ; Sampling Instrument: YSI - handheld multi-parameter instrument; Sampling and Analyzing Method: Station is approached slowly to ensure that the deceleration of the boat does not create a wake and resuspend sediments into the water column. All hydrographic and water column measurements are collected while the vessel is set to drift over the station to minimize interference from sediment plumes generated from physical disturbances of the bottom. Sonde deployment, water transparency and water sample collection must occur within 5 m of the station location. Measurements are made in the following order: (1) PAR, (2) visibility, (3) hydrography, (4) water samples, (5) depth, (6) biomass cores. While taking measurements, care is taken not to disturb the sediment or agitate seagrasses. The sonde is lowered so that the instrument probes are completely submerged.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: SEA GRASSES - DENSITY (measured); Units: shoots/m2; Observation Category: in situ; Sampling Instrument: PVC corer; Sampling and Analyzing Method: Three replicate cores are used for estimates of above- and below-ground biomass. A 15 cm inner diameter (ID) core is used to sample Thalassia, and a 9 cm ID core is used to sample Halodule, Syrindogium, Ruppia and Halophila. Seagrass species composition is determined by visual in situ analysis of plants observed within a 25 m radius of each site. A PVC (polyvinyl chloride) core is used for the collection of below-ground and above-ground material. Care is taken to keep only the shoots that reside within the diameter of the core. Following placement of the 15 cm core on the seabed, the rubber stopper is removed from the top of the core. For both 9 cm and 15 cm cores, before pressing the core into the sediment, the diver runs their fingers carefully around the bottom of the core. If grass has been pulled under the core, it is removed. The diver then presses and twists the core down into the sediment (10-15 cm depth). The stopper is re-installed in the 15 cm core, and the core rocked back and forth. The diver then works their hand under the core and removes it from the grass bed, making sure to keep their hand under the bottom of the core in order to prevent loss of sample. After emptying the core into a sieve, broken shoots are removed, since these are likely exterior shoots that were cut by the core tube. Samples are then placed in pre-labeled Ziploc bags and immediately placed on ice. In the lab, plants are counted, divided into above and belowground portions, and massed after being dried to a constant weight at 50 C. Values are extrapolated to shoots/m2.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: SEA GRASSES - BIOMASS (measured); Units: grams/m2; Observation Category: in situ; Sampling Instrument: PVC corer; Sampling and Analyzing Method: Three replicate cores are used for estimates of above- and below-ground biomass. A 15 cm inner diameter (ID) core is used to sample Thalassia, and a 9 cm ID core is used to sample Halodule, Syrindogium, Ruppia and Halophila. Seagrass species composition is determined by visual in situ analysis of plants observed within a 25 m radius of each site. A PVC (polyvinyl chloride) core is used for the collection of below-ground and above-ground material. Care is taken to keep only the shoots that reside within the diameter of the core. Following placement of the 15 cm core on the seabed, the rubber stopper is removed from the top of the core. For both 9 cm and 15 cm cores, before pressing the core into the sediment, the diver runs their fingers carefully around the bottom of the core. If grass has been pulled under the core, it is removed. The diver then presses and twists the core down into the sediment (10-15 cm depth). The stopper is re-installed in the 15 cm core, and the core rocked back and forth. The diver then works their hand under the core and removes it from the grass bed, making sure to keep their hand under the bottom of the core in order to prevent loss of sample. After emptying the core into a sieve, broken shoots are removed, since these are likely exterior shoots that were cut by the core tube. Samples are then placed in pre-labeled Ziploc bags and immediately placed on ice. In the lab, plants are counted, divided into above and belowground portions, and massed after being dried to a constant weight at 50 C. Values are extrapolated to g/m2.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: SALINITY (measured); Units: unitless; Observation Category: in situ; Sampling Instrument: YSI - handheld multi-parameter instrument; Sampling and Analyzing Method: Station is approached slowly to ensure that the deceleration of the boat does not create a wake and resuspend sediments into the water column. All hydrographic and water column measurements are collected while the vessel is set to drift over the station to minimize interference from sediment plumes generated from physical disturbances of the bottom. Sonde deployment, water transparency and water sample collection must occur within 5 m of the station location. Measurements are made in the following order: (1) PAR, (2) visibility, (3) hydrography, (4) water samples, (5) depth, (6) biomass cores. While taking measurements, care is taken not to disturb the sediment or agitate seagrasses. The sonde is lowered so that the instrument probes are completely submerged.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: SALINITY (measured); Units: unitless; Observation Category: in situ; Sampling Instrument: refractometer; Sampling and Analyzing Method: Station is approached slowly to ensure that the deceleration of the boat does not create a wake and resuspend sediments into the water column. All hydrographic and water column measurements are collected while the vessel is set to drift over the station to minimize interference from sediment plumes generated from physical disturbances of the bottom. Sonde deployment, water transparency and water sample collection must occur within 5 m of the station location. Measurements are made in the following order: (1) PAR, (2) visibility, (3) hydrography, (4) water samples, (5) depth, (6) biomass cores. While taking measurements, care is taken not to disturb the sediment or agitate seagrasses. A small water sample is placed onto the refractometer and the salinity is recorded.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: Secchi depth (measured); Units: meter; Observation Category: in situ; Sampling Instrument: Secchi disk; Sampling and Analyzing Method: Station is approached slowly to ensure that the deceleration of the boat does not create a wake and resuspend sediments into the water column. All hydrographic and water column measurements are collected while the vessel is set to drift over the station to minimize interference from sediment plumes generated from physical disturbances of the bottom. Sonde deployment, water transparency and water sample collection must occur within 5 m of the station location. Measurements are made in the following order: (1) PAR, (2) visibility, (3) hydrography, (4) water samples, (5) depth, (6) biomass cores. While taking measurements, care is taken not to disturb the sediment or agitate seagrasses. When using a secchi disk for visibility measurements, sunglasses are removed and care is taken to prevent the vessel from shading the disk.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: WATER TEMPERATURE (measured); Units: degrees Celsius; Observation Category: in situ; Sampling Instrument: YSI - handheld multi-parameter instrument; Sampling and Analyzing Method: Station is approached slowly to ensure that the deceleration of the boat does not create a wake and resuspend sediments into the water column. All hydrographic and water column measurements are collected while the vessel is set to drift over the station to minimize interference from sediment plumes generated from physical disturbances of the bottom. Sonde deployment, water transparency and water sample collection must occur within 5 m of the station location. Measurements are made in the following order: (1) PAR, (2) visibility, (3) hydrography, (4) water samples, (5) depth, (6) biomass cores. While taking measurements, care is taken not to disturb the sediment or agitate seagrasses. The sonde is lowered so that the instrument probes are completely submerged.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: suspended solids (measured); Units: milligram/liter; Observation Category: in situ; Sampling Instrument: bottle; Sampling and Analyzing Method: Replicate water samples were obtained at each station for determination of Total Suspended Solid (TSS) concentration. Bottles and lids are rinsed three times with sample water before collecting the sample. Gloves are worn if the collector is wearing sunscreen to prevent contamination of sample. The TSS method is adapted from EPA Method 160.2. Summary of Method: A well-mixed sample is filtered through a glass fiber filter, and the residue retained on the filter is dried to constant weight at 103-105°C. Sample Handling and Preservation Non-representative particulates such as leaves, sticks, fish, and lumps of fecal matter should be excluded from the sample if it is determined that their inclusion is not desired in the final result. Preservation of the sample is not practical; analysis should begin as soon as possible. Refrigeration or icing to 4°C, to minimize microbiological decomposition of solids, is recommended. Interferences: Filtration apparatus, filter material, pre-washing, post-washing, and drying temperature are specified because these variables have been shown to affect the results. Samples high in Filterable Residue (dissolved solids), such as saline waters, brines and some wastes, may be subject to a positive interference. Care must be taken in selecting the filtering apparatus so that washing of the filter and any dissolved solids in the filter minimizes this potential interference. Laboratory Procedures: 1) Dry new filters at 60°C in oven prior to use. 2) Weigh filter immediately before use. After weighing, handle the filter or crucible/filter with forceps or tongs only. 3) Place the glass fiber filter (i.e. Glass fiber filter discs, without organic binder, such as Millipore AP-40, Reeves Angel 934-AH, Gelman type A/E, or equivalent; Our lab uses 47 mm GF/F 0.7 micron retention) on the membrane filter apparatus. NOTE: Because of the physical nature of glass fiber filters, the absolute pore size cannot be controlled or measured. Terms such as “pore size”, “collection efficiencies” and “effective retention” are used to define this property in glass fiber filters. 4) For a 47 mm diameter filter, filter 100 mL of sample. If weight of captured residue is less than 1.0 mg, the sample volume must be increased to provide at least 1.0 mg of residue. If other filter diameters are used, start with a sample volume equal to 7 mL/cm of filter area and collect at least a weight of residue proportional to the 1.0 mg state above. NOTE: If filtering clear pristine water, start with 1 L. If filtering turbid water start with 100 mL. NOTE: If during filtration of this initial volume the filtration rate drops rapidly, or if filtration time exceeds 5 to 10 minutes, the following scheme is recommended: Use an unweighed glass fiber filter affixed in the filter assembly. Add a known volume of sample to the filter funnel and record the time elapsed after selected volumes have passed through the filter. Twenty-five mL increments for timing are suggested. Continue to record the time and volume increments until filtration rate drops rapidly. Add additional sample if the filter funnel volume is inadequate to reach a reduced rate. Plot the observed time versus volume filtered. Select the proper filtration volume as that just short of the time a significant change in filtration rate occurred. 5) Assemble the filtering apparatus and begin suction. 6) Shake the sample vigorously and quantitatively transfer the predetermined sample volume selected to the filter using a graduated cylinder. Pour into funnel. 7) Remove all traces of water by continuing to apply vacuum after sample has passed through. 8) With suction on, wash the graduated cylinder, filter, non-filterable residue and filter funnel wall with three portions of distilled water allowing complete drainage between washing. Remove all traces of water by continuing to apply vacuum after water has passed through. NOTE: Total volume of distilled rinse water used should equal no less than 50 mLs following complete filtration of sample volume. 9) Carefully remove the filter from the filter support. 10) Dry at least one hour at 103-105°C. Overnight drying ensures accurate filter weight. 11) Cool in a desiccator and weigh. 12) Repeat the drying cycle until a constant weight is obtained (weight loss is less than 0.5 mg). Calculations: TSS (mg/L) is calculated as follows: 1000 x (A-B) x (1000/C) = TSS where A = weight of filter (or filter and crucible) + residue (mg), B = weight of filter (or filter and crucible) (mg), and C = amount of sample filtered (mL).; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: Dissolved Inorganic Nitrogen (measured); Units: micromole/liter; Observation Category: in situ; Sampling Instrument: bottle; Sampling and Analyzing Method: Replicate water samples were obtained at each station for determination of Dissolved Inorganic Nitrogen (DIN) concentration. Bottles and lids are rinsed three times with sample water before collecting the sample. Gloves are worn if the collector is wearing sunscreen to prevent contamination of sample. Samples were processed following Parsons, Maita, and Lalli (1984) Determination of Ammonia (The Alternative Method).; Data Quality Method: Replicate water samples were obtained at each station for determination of Dissolved Inorganic Nitrogen (DIN) concentration. Bottles and lids are rinsed three times with sample water before collecting the sample. Gloves are worn if the collector is wearing sunscreen to prevent contamination of sample. Samples were processed following Parsons, Maita, and Lalli (1984) Determination of Ammonia (The Alternative Method)..
- Parameter or Variable: AMMONIUM (NH4) (measured); Units: micromole/liter; Observation Category: in situ; Sampling Instrument: bottle; Sampling and Analyzing Method: Replicate water samples were obtained at each station for determination of Ammonium (NH4+) concentration. Bottles and lids are rinsed three times with sample water before collecting the sample. Gloves are worn if the collector is wearing sunscreen to prevent contamination of sample. Samples were processed following Parsons, Maita, and Lalli (1984) Determination of Nitrate.; Data Quality Method: Data are checked against reasonable value ranges..
- Parameter or Variable: DISSOLVED OXYGEN (measured); Units: percent; Observation Category: in situ; Sampling Instrument: YSI - handheld multi-parameter instrument; Sampling and Analyzing Method: Station is approached slowly to ensure that the deceleration of the boat does not create a wake and resuspend sediments into the water column. All hydrographic and water column measurements are collected while the vessel is set to drift over the station to minimize interference from sediment plumes generated from physical disturbances of the bottom. Sonde deployment, water transparency and water sample collection must occur within 5 m of the station location. Measurements are made in the following order: (1) PAR, (2) visibility, (3) hydrography, (4) water samples, (5) depth, (6) biomass cores. While taking measurements, care is taken not to disturb the sediment or agitate seagrasses. The sonde is lowered so that the instrument probes are completely submerged.; Data Quality Method: Data are checked against reasonable value ranges..
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