Urea decomposition activities in an ammonium enriched freshwater pond

Abstract

Urea decomposition activities, urea and ammonium concentrations, and the concentration of chlorophyll a (chl a ) were measured in an ammonium enriched, hypertrophic freshwater pond at 5 to 7 h intervals during 3 &el cycles on June 27 to 28, September 6 to 7,1992 and February 14 to 15,1993. The study site was characterized by very high anlmonium concentrations, ranging from 123.6 to 403.6 p M . During the study period, the urea concentration ranged from 1 3 to 9.1 pM and chl a concentration ranged from 81.5 to 211.8 pg 1-'. In 2 of 3 diel cycles the nighttime urea decomposition rate in whole waters was higher than the daytime decomposition rate; in 1 diel experiment the nighttime decomposition rate was 56.4 % of the daytime rate, indicating that the variation of urea decomposition rate was not associated with natural light/dark cycles. Despite the very high ammonium concentrations, substantial urea decomposition rates (5.5 to 80.8 nM h-') were observed, particularly in June and September. Such high decomposition rates were due to high chl a-specific activity rather than due to large phytoplankton biomass and low activity. When urea concentration was high (ca >2 PM), the urea decomposition rate showed a linear increase with increasing urea concentration even in the presence of high ammonium concentrations (range of 123.6 to 403.6 PM), suggesting that elevated urea concentration mitigates the repressive effect of ammonium on urea decomposition. The urea decon~position rate in GF/C filtrates (mainly bacterial-size fractions) ranged from negligible to 39.3 nM h-', representing an average of 47.1 % of the activity in whole pond waters. This study suggests that urea decomposition activity in an ammonium enriched freshwater pond is significantly elevated and controlled by the urea concentration, and that bactena might contribute substantially to urea decomposition rate in a hypertrophic freshwater pond.

Comparative effects of urea, ammonium, and nitrate on phytoplankton abundance, community composition, and toxicity in hypereutrophic freshwaters

“…4). Unfortunately, relatively little is known of how urea uptake kinetics vary among freshwater phytoplankton (Solomon et al 2010), or whether transformation of urea into inorganic N species may alter outcomes of competition for N (Park et al 1997), although empirical results from this and other experiments (Berman and Chava 1999;Finlay et al 2010) suggest that pollution of P-rich waters with urea may stimulate growth of many forms of algae.…”

Diel variation in urea decomposing activity in the euphotic zone of brackish Lake Nakaumi

“…Diel variations in urea decomposition have been observed in lacustrine environments (Webb and Haas 1976;Mitamura and Saijo 1986a;Park et al 1997). Webb and Haas (1976) and Mitamura and Saijo (1986a) recognized higher rates of urea decomposition during the daytime than during the night.…”

“…Urea decomposition by natural phytoplankton has been demonstrated using 14 C-labeled urea (Mitamura and Saijo 1986a;Irmisch 1991;Mitamura et al 1994Mitamura et al , 1995Tamminen and Irmisch 1996;Park et al 1997). Urea decomposition by natural phytoplankton has been demonstrated using 14 C-labeled urea (Mitamura and Saijo 1986a;Irmisch 1991;Mitamura et al 1994Mitamura et al , 1995Tamminen and Irmisch 1996;Park et al 1997).…”

Urea: a nitrogen source for the aquatic resurrection plant Chamaegigas intrepidus Dinter

“…Average ammonium concentrations were generally lower by an order of magnitude than the values found for hypertrophic freshwater ponds (100-400 µM; Park et al 1997) and only slightly higher than in mountain lakes of central Europe (5-30 µM; Kopácek et al 1995). These observations suggest that urea could be an important source of nitrogen in the rock pools.…”

“…The average concentration of urea in the rock pools was found to be in the range 20-30 µM, which is substantially higher than in a hypertrophic freshwater pond (1-9 µM; Park et al 1997). Average ammonium concentrations were generally lower by an order of magnitude than the values found for hypertrophic freshwater ponds (100-400 µM; Park et al 1997) and only slightly higher than in mountain lakes of central Europe (5-30 µM; Kopácek et al 1995).…”