16 research outputs found
Nutrient limitation of periphyton growth in arctic lakes in south-west Greenland
This article is distributed under the terms of the
Creative Commons Attribution License which permits any use, distribution,
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
Spatio-temporal variability and controls on methane and nitrous oxide in the Guadalquivir Estuary, Southwestern Europe
Estuaries are significant methane (CH4) and nitrous oxide (N2O) emitters, although dynamics of both greenhouse gases in these ecosystems are regulated by complex processes. In this work, we aimed at characterizing the spatio-temporal distribution of CH4 and N2O in the Guadalquivir river estuary (SW Spain), the southernmost European estuary. During eight sampling cruises conducted between 2016 and 2017, surface water CH4 and N2O concentrations were measured along the salinity gradient of the estuary by using static-head space equilibration gas chromatography. The CH4 and N2O saturation ranges over the estuarine transect were 520â30,800% (average 2285%) and 40â390% (average 183%), respectively and airâwater fluxes ranged from 13 to 1000 ”mol mââ2 dayââ1(average 66.2 ”mol mââ2 dayââ1) for CH4 and from ââ7 to 35 ”mol mââ2 dayââ1 (average 8.5 ”mol mââ2 dayââ1) for N2O. A slight increase in the emissions was detected upstream and no seasonal trends were observed. Mixing between freshwater and oceanic waters influenced biogeochemistry of estuarine waters, affecting CH4 and N2O fluxes. In order to identify potential sources of CH4 and N2O, biogeochemical parameters involved in the formation pathways of both gases, such as salinity, dissolved oxygen, nutrients and organic matter were analyzed. Results suggested that sulfate inhibition and microbial oxidation played a relevant role in dissolved CH4 accumulation in the water column whereas associations found between N2O, nitrate and oxygen indicated that nitrification was a major source of this gas. Therefore, the influence of the tidal-fluvial interaction on ecosystem metabolism regulates trace gas dynamics in the Guadalquivir estuary.This research was funded by the project 1539/2015 from the Spanish Ministry for Agriculture, Food and Environment.Peer reviewe