B A Crosby | PubMed Health

PubMed2000

Comparing and assessing acid rain-sensitive ponds.

Changes in pH and temperature were monitored in two freshwater ponds in Southeastern Massachusetts from 1990 to 1993 using a remote-sensing system that collected data on a continuous basis. The sensing system included a combination electrode, pH meter and portable computer powered by a marine battery. Temperature and pH information from the pH meter were acquired every 10 min and stored in the computer. The two ponds, located within 2 km of one another, have a different average pH and sensitivity to acid precipitation. Maquan Pond has an average pH of 6.0 and an alkalinity of 7.4 mg/l, while Furnace Pond has an average pH of 6.9 and alkalinity of 14.9 mg/l. The pH of both ponds varied seasonally and showed diel changes due to the photosynthetic and respiratory activity of aquatic organisms. Precipitation events did not change the pH of Furnace Pond. Maquan Pond on the other hand, did exhibit changes in surface water pH due to specific acidic precipitation events. During certain rainstorms, the pH of Maquan surface waters dropped to values as low as pH 4. In addition to the transient changes in pH, the acid-sensitive pond also exhibited differences in planktonic distribution patterns.

Acid Rain↗

PubMed1995

Segmental chloride transport in the Dahl-S rat kidney during L-arginine administration.

L-Arginine normalizes pressure natriuresis in Dahl salt-sensitive (DS) rats. The nephron segments responsible for improvement in sodium chloride handling during L-arginine administration are unknown. Micropuncture techniques were used to examine fluid and chloride transport along superficial nephron segments in DS rats maintained on an 8% sodium diet and given L-arginine or vehicle ip for 3 wk. Renal perfusion pressure in vehicle-treated DS rats was reduced to that of L-arginine-treated DS rats with an aortic snare. Dahl salt-resistant (DR) rats receiving vehicle were examined for comparison. In agreement with previous studies, urinary sodium chloride excretion was greater (P < 0.05) in L-arginine DS rats than in vehicle DS rats and not different from DR rats at equivalent renal perfusion pressures. Whole-kidney and single-nephron GFR were not different (P = not significant) among groups. Fractional proximal tubule chloride and fluid reabsorption was not different among groups. Fractional loop chloride reabsorption was greater in vehicle-treated DS rats than in DR rats (58.5 +/- 1.5 versus 46.6 +/- 1.7%; P < 0.05), confirming the enhanced chloride reabsorption at this location in DS rats previously reported. Fractional loop chloride reabsorption was identical in vehicle- and L-arginine-treated DS rats (58.4 +/- 1.4 versus 58.9 +/- 3.9%; P = not significant). Fractional loop fluid reabsorption was not different among groups. Fractional distal fluid and chloride reabsorption was not different between DS rat groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗