| Description: | (Methods from thesis)
Limnologic Parameters
Physical, chemical, and biological aspects of the study area were sampled on the following dates: November 4-5, 1999; December 7-9, 1999; February 17-18, 2000; April 20-21, 2000; July 14-15, 2000; August 15-17, 2000; July 7-12, 2001; August 4-6, 2001 and; September 1-2, 2001. Seasons were defined as: December and February (Winter); April (Spring); July and August (Summer); and September and November (Fall). River flow and reservoir hydraulic retention times (total volume / outflow rate) were calculated using USGS gauging station data at Rocky Reach Dam (station 12453700). Reservoir water level elevations were downloaded from the “DART River Environment” website (DART 2002). Temperature (YSI ® 57), dissolved oxygen (YSI ® 57), and specific conductance (YSI ® 30) were measured with calibrated meters and probes. Transparency and light penetration were measured with a standard 20 cm Secchi disk and calibrated LiCor ® photometer. Flow measurements were taken with a Marsh-McBirney ® flowmeter. Dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), nitrate (NO3), nitrite (NO2), ammonia / ammonium (NH4 + NH3), total nitrogen (TN), total phosphorus (TP), and pH measurements of the water column were obtained from a concurrent pelagic study (Rensel et al. 2001). Nutrient concentrations were determined from composite samples taken with an integrated sampling tube from depths of 1 m to mid-water column.
Epilithic Algae
Epilithic algae were sampled from littoral rocks (natural substrates) along with water column parameters. At one sampling event, 10 epilithic algae samples were taken from each riverbank (20 samples per site) for a total of 120 epilithic algae samples per time. At each riverbank, nine of the samples were used for pigment / biomass analysis and one was used for taxonomic identification. Riverbanks were designated left or right when facing downstream. Samples at each bank were split into two depth zones, five replicates from the A zone and five replicates from the B zone. The A zone was defined as the zone of water level fluctuation relative to full pool (0-1 m) and the B zone was defined as the permanently wetted zone (>1 m water depth relative to full pool).
Within each depth zone epilithic algae samples were obtained from relatively flat stones by random dredging (Petite Ponar and Petersen dredges). Epilithic algae was scraped from a 0.0220 m2 area from the top of the stone, then carefully washed into a clean centrifuge tube. The area scraped was determined following past epilithic algae studies on the Mid-Columbia and Lower Snake River (Falter and Kraemer 2000; Kraemer 2000). All epilithic algae samples were stored on ice and in the dark. Epilithic algae composition samples were stored in 50 ml centrifuge tubes and preserved with Lugol’s iodine solution at a ratio of one part iodine solution to five parts water / epilithic algae. Composition samples were stored at 4º C. The night following collection, the pigment and biomass samples were membrane-filtered onto Whatman (GF/C 47mm diameter, 1.2 µm pore size) ashless filters and stored at 4º C in the dark. Upon returning from the field, pigment and biomass samples were frozen and stored for a maximum of six months before processing.
Pigment / biomass samples were individually cut in two equal portions using a template. One half was macerated with a tissue grinder and steeped in MgCO3 saturated acetone for 24 hrs before pigment analysis. Chlorophyll and pheophytin were measured with a Beckman ® Model DU-640 spectrophotometer. Monochromatic chlorophyll a, pheophytin, trichromatic chlorophyll a, b, and c were determined according to APHA (1992) standard method 10200 H (1-2). The other half of the split sample was used for gravimetric biomass analysis. Oven-dry weight (ODW) and ash-free oven-dry weight (AFODW) were determined using the gravimetric method described by APHA (1992) standard method 10200 I (5). This method does not indicate photoautotrophic biomass as directly as chlorophyll analysis since organic material from epilithic heterotrophs or decomposing organics is included in the AFODW. For this reason the term epilithic biofilm is used to describe AFODW and ODW.
The autotrophic index was calculated by dividing the AFODW of a sample by its corresponding chlorophyll a (monochromatic or trichromatic) content. Algal species composition was determined to genus or nearest taxon (Prescott 1964) with a Wild ® M20-704479 compound light microscope at 150 times magnification. Using APHA (1992) standard method 10200 F (b) for intermediate magnification, algal cells were enumerated and identified. This was done with a Palmer-Maloney counting chamber and Whipple disk with micrometer-calibrated fields of vision.
Chlorophyll accrual rates on artificial substrates were used as a surrogate for rates of epilithic algae primary production. These were deployed in July and August of 2001. The artificial substrates were allowed to incubate for 30 days in the permanently wetted littoral of each site on both riverbanks. Three artificial substrates were deployed near each riverbank. An artificial substrate consisted of one, square (15 cm × 15 cm), unglazed, terra cotta tile fastened to the top of a masonry brick resting on the bottom. The three artificial substrates were placed to have similar flow, aspect, and depth. Artificial substrates were deployed and retrieved with snorkeling gear. After slow retrieval to minimize current scouring, the light-exposed tile surface (0.0225 m2) was scraped with a razor blade and attached growth dispensed into a centrifuge tube as before. Area scraped again determined by following previous attached algae work by Kraemer (2000). Analysis of chlorophyll pigments and biomass proceeded as described for natural substrates.
Sub-Littoral and Pelagic Zone Sediments
Dredged sediment samples were collected on: July 14-15, 2000; August 15-17, 2000; July 11-12, 2001; and August 4-5, 2001. In 2000, sediments were sampled in suspected depositional zones (eddies and thalweg) at each site. During 2000 sampling, every site except the tributary site (Entiat River) had dredges taken in three areas. Two were suspected depositional areas near each riverbank and the other was the channel thalweg. At one of these sampling points, dredging was continued until three successful dredges were taken. A dredge was considered successful when the dredge hit the bottom squarely, closed properly, and yielded either a totally empty or full dredge sample. Some sediment and benthic substrate was too large to collect (stones > 0.25 m). Some of the 2000 sediment samples were combined into a composite sample and homogenized before storage because of a small sediment return with some dredges. In 2001 a systematic sampling approach was used by dredging along a transect perpendicular to the shoreline at 10 m increments at each site except for the Entiat River where dredges were taken every 3 m. Since sampling procedures differed during summer 2000 and 2001, some results from both years were combined.
All sediment dredging was done with a weighted, petite Ponar dredge (225 cm2 surface area) and electric winch. Upon retrieval of dredges, in the field, particle size was estimated by the modified Wentwoth scale (Cummins 1962); observation of any organisms present (aquatic macrophytes or benthic in-fauna); sediment color pattern; and sediment smell (no smell, putrid, or H2S). Along with those qualitative characteristics, the oxidation / reduction (redox) potential, temperature, and pH of the fine sediments were measured according to chapter 5.2.1 of Murdoch and Azcue (1995). These sediment characteristics where measured with an Orion ® pH / Eh meter with temperature probe. Calibrated Orion ® Pt / AgCl2 redox and Orion Sureflow ® pH probes were immediately inserted into an undisturbed dredged sample and allowed to equilibrate for 5 to 10 minutes. Field redox potentials were corrected for temperature and electrode response to Zobell’s standard reading (Kehew 2001).
After field measurements, dredged samples were stirred and placed into a quart size sealable plastic freezer bag. Sediment samples were stored at 4º C for up to 72 hr until freezing at lab for later processing. In preparation for analysis, sediment samples were thawed and oven-dried at 65º C for at least 24 hr. After drying, samples were hand ground and separated into two portions, one for particle size analysis and the other for gravimetric biomass analysis. Particle size was determined using 100 g of sieved, dispersed, and temperature-compensated sediment by the Bouyoucos method (1962). Particle size was reported as percent sand (2.0-0.05 mm), silt (0.05-0.002 mm), and clay (< 0.002 mm). Gravimetric biomass analysis included oven drying ≈ 15 g of previously dried and ground sediment at 105º C for 14 hr or until constant ODW. This was followed by combusting all organic matter in a muffle furnace at 505º C for one hr (AFODW). AFODW divided by ODW gave percent organic matter.
In addition to dredged sediments, sediment traps were deployed in July and August, 2001. In July, one sediment trap was deployed at each site near shore in 2-3 m of water. In August three sediment traps were deployed at Wells tailrace and Daroga Park. Sediment traps were placed in low velocity (≈ 0 m/s) water at 2-3 m depth near shore by snorkeling divers. Care was taken to avoid suspending sediments during deployment and recovery. Sediment traps consisted of a steel rack containing six PVC cylinders (35.6 cm × 8.1 cm) with plate bottoms (Falter and Burris 1996). Five cylinders were placed upright to measure the sedimentation rate from the water column. One cylinder faced down to act as a control for attached growth on the inside of the cylinder and upward flux of sediment.
Sediment traps were in place for 30 days. Upon retrieval, the cylinders were capped and brought to the surface. Most of the water was drained from cylinders then the remaining sediments were resuspended. The resuspended sediment was completely drained into a 1 L Cubitainer ® and placed on ice until freezing. Gravimetric biomass analysis was performed on the trapped sediment as described with dredged sediment. All trapped sediment was oven-dried and combusted to calculate deposition rates for ODW, AFODW, and percent organic matter. |
