27 research outputs found
Contrasting biogeochemical characteristics of the Oubangui River and tributaries (Congo River basin)
Nutrient limitation of periphyton growth in arctic lakes in south-west Greenland
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and reproduction in any medium, provided the original
author(s) and the source are credited.Many arctic lakes are oligotrophic systems
where phototrophic growth is controlled by nutrient supply.
Recent anthropogenic nutrient loading is associated with
biological and/or physico-chemical change in several lakes
across the arctic. Shifts in nutrient limitation (nitrogen (N),
phosphorus (P), or N ? P) and associated effects on the
growth and composition of algal communities are commonly
reported. The Kangerlussuaq region of south-west
Greenland forms a major lake district which is considered
to receive little direct anthropogenic disturbance. However,
long-range transport of pollutant N is now reaching
Greenland, and it was hypothesised that a precipitation
gradient from the inland ice sheet margin to the coast might
also deliver increased N deposition. In situ nutrient bioassays
were deployed in three lakes across the region: ice
sheet margin, inland (close to Kangerlussuaq) and the coast
(near Sisimiut), to determine nutrient limitation of lakes
and investigate any effects of nutrients on periphyton
growth and community composition. Nutrient limitation
differed amongst lakes: N limitation (ice sheet margin), N
and P limitation (inland) and N ? P co-limitation (coast).
Factors including variation in N supply, ice phenology,
seasonal algal succession, community structure and
physical limnology are explored as mechanisms to explain
differences amongst lakes. Nutrient limitation of arctic
lakes and associated ecological impacts are highly variable,
even across small geographic areas. In this highly sensitive
region, future environmental change scenarios carry a
strong risk of significantly altering nutrient limitation; in
turn, potentially severely impacting lake structure and
function
Temperature effects on periphyton, epiphyton and epipelon under a nitrogen pulse in low-nutrient experimental freshwater lakes
The ongoing global climate change involves not only increased temperatures but may also produce more frequent extreme events, such as severe rainfall that could trigger a pulse of nutrients to lakes. In shallow lakes, this may affect primary producers through a number of direct and indirect mechanisms. We conducted a six-month mesocosm experiment to elucidate how periphyton (on inert substrata), epiphyton and epipelon biomass responded to a nitrogen (N) pulse, an approximately tenfold enrichment of the NO3-pool, under three contrasting warming scenarios: ambient temperature and ca. +3°C and ca. +4.5°C elevated temperatures (hereafter T1, T2 and T3). After the N pulse, we found a higher periphyton biomass at elevated than at ambient temperatures but no change in epiphyton biomass. Epipelon biomass was lower in T3 than in T1. Both periphyton and epiphyton biomasses correlated negatively with snail biomass, while epiphyton biomass correlated positively with light. Different responses to higher temperatures under short-term extreme nutrient loading conditions may be attributed to differences in the access to nutrient sources and light. Our data suggest that the biomass of periphyton in oligotrophic clear-water lakes will increase significantly under conditions exhibiting short-term extreme nutrient loading in a warmer climate.Fil: Cao, Yu. University Aarhus; Dinamarca. Chinese Academy of Sciences; RepĂşblica de ChinaFil: Olsen, Saara. Sino-danish Centre For Education And Research (sdc); China. University Aarhus; DinamarcaFil: Gutierrez, Marìa Florencia. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Santa Fe. Instituto Nacional de LimnologĂa. Universidad Nacional del Litoral. Instituto Nacional de LimnologĂa; ArgentinaFil: Brucet, Sandra. Institucio Catalana de Recerca I Estudis Avancats; . University Aarhus; Dinamarca. Universitat de Vic;Fil: Davidson, Thomas A.. University Aarhus; DinamarcaFil: Li, Wei. Chinese Academy of Sciences; RepĂşblica de China. Sino-danish Centre For Education And Research (sdc); ChinaFil: Lauridsen, Torben L.. University Aarhus; Dinamarca. Sino-danish Centre For Education And Research (sdc); ChinaFil: Søndergaard, Martin. University Aarhus; DinamarcaFil: Jeppesen, Erik. University Aarhus; Dinamarca. Sino-danish Centre For Education And Research (sdc); Chin