Measurements of phytoplankton primary production by means of the acidification and bubbling method

147

108

Thau lagoon is a Mediterranean shellfish ecosystem with large biomasses of oysters growing in waters with high residence time due to low tidal ranges. The influence of filter feeders (oysters and their epibiota) on the spatial distribution of particulate and dissolved compounds in the water column of Thau lagoon was studied through its variation with time. In 1991/1992, daily variations were investigated in pens, corridors and outside shellfish farming zones for nutrients, chlorophyll a and primary production. Salinity, dissolved oxygen, nutrients, organic matter and chlorophyll a were also monitored in surface waters inside and outside shellfish farming zones each week from January 1993 to March 1994. The presence of shellfish farms led to a decrease by only a few percent of oxygen concentrations in their vicinity, but the mean (± SE) deficits of chlorophyll a and POC concentrations were 44 ± 4% and 26 ± 9% respectively in the eastern zone (8 m). The shift induced by filter feeders in phytoplankton composition favoured picophytoplankton with higher growth rates. But the summer increase in phytoplankton growth rate was stronger than the positive feedback due to filter feeder filtration. Summer was determinant for the growth of oysters owing to enhanced regenerated primary production. During this period, filter feeders were not food limited, while they tended to control phytoplankton biomasses and production the rest of the year. The nutrient excess in shellfish farming zones was highly significant, with increases of 73 ± 16, 36 ± 12 and 19 ± 8% for ammonia, phosphates and silicate respectively in the eastern zone. In the western zone, the nutrient excess was less strong by half for ammonia and phosphate, because the lower depth (4 m) allows light to reach the bottom and enables benthic macroflora to grow on nutrients of benthic origin. The decline of phytoplankton biomasses in shellfish farms induced a decrease in the nutrient demand, especially for ammonia. This situation was likely to favour nitrification, which led during autumn to higher nitrate concentrations within shellfish farming zones than outside. Therefore, filter feeders were able to alter the dominant biogeochemical process in the water column by stimulating nitrification. KEY WORDS: Suspension-feeding bivalves · Phytoplankton · Nutrient cycling · Carrying capacity · Thau lagoonResale or republication not permitted without written consent of the publisher

Section: Methodsmentioning

confidence: 99%

Influence of shellfish farming activities on the biogeochemical composition of the water column in Thau lagoon

Souchu

Vaquer²,

Collos³

et al. 2001

147

108

“…In the latter case, 5 m1 were gently filtered (by gravity or c 8 0 mm Hg vacuum pressure) and the filtrate collected in scintillation vials. T014C and DO14C samples were acidified with 1 m1 HCl (6M or 1M) and either left open in an orbital shaker for 12 h or bubbled with air for approximately half an hour (Riemann & Jensen 1991) for eliminating inorganic I4C. Subsequently, 10 to 17 ml of scintillation cocktail was added to the vials.…”

Section: Methodsmentioning

confidence: 99%

A comparison between glass fiber and membrane filters for the estimation of phytoplankton POC and DOC production

Morán¹,

Gasol²,

Arı́n³

et al. 1999

We tested the performance of 2 types of glass fiber filters (GF/F: 0.7 pm; GF/C: 1.2 pm) and 2 membrane filters (PC0.2: polycarbonate 0.2 p; CE0.22: mixed cellulose esters 0.22 pm) in estimating chlorophyll a and primary production with the 14C technique. Four experiments were carried out with water samples from the NW Mediterranean, the NE Atlantic and the Antarctic Ocean. The first experiment compared measurements of particulate organic carbon (POC) production whereas the other 3 also considered total (TOC) and dissolved (DOC) carbon fixation. No significant differences among filters were found regardmg chlorophyll a retention but large discrepancies existed in the amount of labelled organic carbon retained in all the experments. Both types of glass fiber filters, especially GF/F, yielded higher values of apparent P014C recovery than the membrane filters. The GF/Fderived POC production rates were up to twice the PC0.2-derived rates and 63 % higher than CE0.22-derived ones. Accordingly, the estimated rates of phytoplanktonic DOC production were higher with the membrane filters in comparison to the GF/F ones. This discrepancy was attributed to a high D0I4C adsorption to the glass fibers of GF filters. Due to uncertainties in the magnitude of t h s process in other samples, we conclude that GF filters are not suitable when particulate primary production must be measured without interference of released dissolved products, and that membrane filters should be used instead.

“…At each sampling, 25 m1 subsamples were filtered through at 20 pm mesh net, followed by a 2 Fim Nuclepore filter and a 0.45 pm Sartorius membrane filter. A subsample of 10 m1 was assayed for total primary production by means of a modification of the acidification and bubbling procedure (Schindler et al 1972, Riemann & Jensen 1991. Instead of bubbling, the acidified samples were stored open for 24 h (Riemann & Jensen 1991).…”

Section: Methodsmentioning

confidence: 99%

“…A subsample of 10 m1 was assayed for total primary production by means of a modification of the acidification and bubbling procedure (Schindler et al 1972, Riemann & Jensen 1991. Instead of bubbling, the acidified samples were stored open for 24 h (Riemann & Jensen 1991). The filters were treated with fuming HCl for 5 min.…”

Section: Methodsmentioning

confidence: 99%

Incorporation of viruses into the budget of microbial C-transfer A first approach

Bratbak¹,

Heldal²,

Thingstad³

et al. 1992

199

158

Viral lysis of bacteria has been suggested to be a quantitatively important process in the removal of bacteria, and potentially also in the production of DOC, in the ocean. In order to investigate the quantitative role of viruses in the pelagic microbial ecosystem, a die1 study was undertaken, comprising measurements of particulate and dissolved primary production, bactenal production, bacterial grazing by flagellates, bacterial lysis by viruses, and production of viruses. Estimates of algal excretion (4.7 pm01 C 1-' d-I) and bacterial carbon consumption (3.0 pm01 C I-' d-l) were in reasonable balance. Predation (2.9 pm01 C 1-' d-l) exceeded bacterial production (1.5 pm01 C 1-' d-l) estimates by a factor of 2. Major difficulties in balancing the budget emerged however, from the estimates of vual lysis of bacteria (9.2 pm01 C I-' d-l), which exceeded bacterial production by a factor of 6. Despite these problems, results support the idea that viral lysis may b e a quantitatively significant process that needs to b e incorporated into budgets of microbial C-transfer.