Oxygen pronles (Ward Hunt Island and Resolute) and pH profiles pesolute) were rneasured in the microbial mats located in 15 cm of water in the littoral zone of the lake. TLVO to
h e e profles were made at each of the three sites at depth intervals of 125 Fm. The measurements were made with 2 mm diameter micro-electrodes ( L a m Research Labs, hc.) k e d to a micromanipuiator consisting of a microburette fixed to a metallic suppon and installed on a small wooden base in order to obtain in situ profiles. A survey of pH and O2 was done at each site by taking measurements at the surface and inside the mats. The oxvgen probe was calibrated for 100 % saturation with a saline solution (NaCl 0.02 iLI) thar had been allowed to equilibrate with atmosphere. The zero point was obtained with the same saline solution that was
driven to zero oxygen by bubbling with an inert gas (nitrogen). Temperature dataloggers were instdled under and just above the mat at site E2 to measure temperature continuously throuehout the sampling period at Ward Hunt Lake. The presence of small rocks and gas bubbles made profilhg difficult and we therefore obtained a variable number of profiles at each site. The cohesiveness of the mats also varied and influenced the accuncy of profiling.
Nutrients
and
major ionsWater samples were collected in triplicale at three locations for each site at Ward Hunt Lake: surface lakewater (SL); surface of the mat (MS); and interstitiai water within the mat (MI).
SL and MI samples were also collected at the Resolute sites, specifically for nutrient analysis.
MS samples were fiom the 5 mm-layer of water immediately overlying the microbiai mats.
This
boundary layer was sampled with a purnping system consisting of a hand pump and a plastic tube fixed to a 22-cm diameter plexiglas disk to limit the sampling to the water just above the mat (Fig. 1.2).
This
microlayer sarnpler vas introduced slowly in the water and subsequentiy laid down gently on the mat d a c e in order not to disrupt the boundary layer. The SL and MS samples fiom water column were collected in triple-rinsed Nalgene bottles, and stored in the cold and dark for up to 2 h prior to filtration.For the MI analyses, individual mat sections (100 cm') were taken and placed in a Whirlpak plastic bag that had been rinsed three times with lakewater. The interstitial water was gently expressed fiom the mat by exerting light pressure, and this water was then transferred to a
plastic disk
Figure 2.2 Pumping system used to sample the boundary Iayer overlying microbial mats.
vial. In order to eliminate bacterial decomposition, 5 pl of rnercuric chloride 1% (HgC12) were added to the MI samples.
SL
and MS samples were filtered through GFlF filters and were stored at < j°C for subsequent chemical analysis of dissolved organic carbon @OC), total dissolved nitrogen(TDN),
nitritehitrate-N (NO2MO3-N), ammonia-nitrogen (NH3-N) and soluble reactive phosphonis(SRP).
The MI samples were subsequently sedimented and the supernatant filtered through Whatman glass fibre (grade GFE) filten (DOC, TDN? N02/N03-N, MI3-N and SRP) or through cellulose acetate filters (0.45 pm) fixed to a syringe (total dissoived phosphorus analysis; TDP).
n e major ion analysis was performed on unfiitered samples with the exception of M S samples which were GFE-filtered. The bfI and MS samples were subsequently diluted with deionized water for the nutrient (MS 13.4, MI 120) and major ion (bIS 1:20, MI 150) analyses. However.
the samples fiom site
R3
were M e r diluted (1 : 100. final concentration) because of particles that remained in suspension in the LW extract. The TP sarnples were preserved by the addition of lm1 of 30% H2S04 to each 100 ml of water. The nutrient and major ion analyses were performed by the National Laboratory for Environmental Testing (Environment Canada Burlington. Ont.) using methods given in Environment Canada (1998). Dissolved inorganic carbon (DIC) was estimated by Gran titration (Wetzel & Likens 1991) in all samples. The MI sarnples were allowed to sediment for 30 mins prior to timtion. No filtration was done for this anaiysis because this process c m lead to an incorporation of the ambient CO?. However, the DIC values are likely to be over-estimates because some of particulate inorganic carbon (PIC) could have remained in suspension in the samples, and have contributed to the total DIC measured. To evaluate the proportion of PIC in the samples, we filtered a known volume of MI sarnple (2 to 5 ml) through a GFIF filter. This filter was then placed in 20 ml of deionized-distilled water during 24 hours andthe resultant solution then titrated. For the Resolute samples, we used a different method for the preparation of sarnples for titration because we obtained some irregular curves during the titration of the MI, suggesting interference by PIC. We diluted a sub-sample of MI with deionized- distilled water, allowed any PIC to dissolve for 1 h and then made the usual titration.
Periphyton sampling
Cores of the microbial mats were coilected at each site for biological analysis according a random sampling plan within a 1 rnZ quadrate. The cores were 16 mm diameter and were sampling Uito upper (orange-brown color) and lower (blue-greenish) layes, and each section was then preserved fiozen in aluminium foi1 until extraction and analysis up to two mondis later. A solvent m i m e of 911 (v/v) acetone-water was used for pigment extraction, following the recornmendations by Downes et al. (1993) for htarctic microbial mats. In order to improve rhe extraction efficiency for pigments, we evaluated the effect of the extraction time and also the number of -ginding-solvent extraction sequences. The &gindine was done using a Teflon tissue k n d e r , (Cafiamo mode1 RZRI). A piece of GFE filter was added to each core sample to help extraction produced a much smaller quantity of additional pigment. We therefore adopted a nvo step extraction protocol, which is likely to underestimate Ch1 a by c. 20 % and carotenoids by c.
28 %.
After the preliminary tests the following protocol was adopted. Each core was ground in 8 ml 9: 1 acetone-water and left to extract for 1 h at 4°C in the dark. The samples were then shaken by inversion and centrifuged 10 minutes at 1000 rpm. The supernatant was decanted and the absorbance at 663 nm and 750 nm then measured by spectrophotomeûy (Miion Roy Spectronic 1001 plus). The absorbance measurements were made before and afler acidification, the latter done by adding 2 drops of HCI 4N and maintainhg the sarnples for 30 minutes at 4OC in the dark.
The pellet was then resuspended in 9:l acetone and this process repeated. The results fiom the
two extractions were then summed, with a correction for the amount of solvent contained within the pellet. Ch1 a concentrations were caiculated fiom the equation of Golterman (1971) and carotenoids were calculated fiom Stickland & Parsons (1 972) and Elritton (1985).
Water column samples were collected in Naigene plastic botties tiom each site at Ward Hunt Lake at 1 rn from the shore, just beneath the surface. The samples were filtered within 2 h ont0 GF/F filters and the filten were stored fiozen until subsequent analysis. The extraction was performed up to two months later by placing the filters in boiling ethanol (95 %) and the Chl a fluorescence then measured in the extract by fluometry (Sequoia-Tuer mode1 450 fluorneter with the standard CM a filter set) before and after acidification. Ch1 a concentrations were calculated using the equation of Nusch (1980).
The Ch1 a concentrations were used as a measure of aurotrophic mat biomass for samples fiom the two locations, while ah-free dry weight was used to evaiuate total microbial biomass.
Cores for the latter analysis were wrapped in aluminium foi1 and presemed fkozen until analysis.
Each core was subsequently dned at 80°C for 48 hours and then weighed before and afier ignition at 480°C for 12 houn (modified k o m Wetzel 1983). The ash-fiee dry weight analysis
was performed only for the sites at Ward Hunt Lake.