TY  - JOUR
A1  - Giling, Darren P.
A1  - Nejstgaard, Jens C.
A1  - Berger, Stella A.
A1  - Grossart, Hans-Peter
A1  - Kirillin, Georgiy
A1  - Penske, Armin
A1  - Lentz, Maren
A1  - Casper, Peter
A1  - Sareyka, Joerg
A1  - Gessner, Mark O.
T1  - Thermocline deepening boosts ecosystem metabolism: evidence from a large-scale lake enclosure experiment simulating a summer storm
JF  - Global change biology
N2  - Extreme weather events can pervasively influence ecosystems. Observations in lakes indicate that severe storms in particular can have pronounced ecosystem-scale consequences, but the underlying mechanisms have not been rigorously assessed in experiments. One major effect of storms on lakes is the redistribution of mineral resources and plankton communities as a result of abrupt thermocline deepening. We aimed at elucidating the importance of this effect by mimicking in replicated large enclosures (each 9 m in diameter, ca. 20 m deep, ca. 1300 m 3 in volume) a mixing event caused by a severe natural storm that was previously observed in a deep clear-water lake. Metabolic rates were derived from diel changes in vertical profiles of dissolved oxygen concentrations using a Bayesian modelling approach, based on high-frequency measurements. Experimental thermocline deepening stimulated daily gross primary production (GPP) in surface waters by an average of 63% for > 4 weeks even though thermal stratification re-established within 5 days. Ecosystem respiration (ER) was tightly coupled to GPP, exceeding that in control enclosures by 53% over the same period. As GPP responded more strongly than ER, net ecosystem productivity (NEP) of the entire water column was also increased. These protracted increases in ecosystem metabolism and autotrophy were driven by a proliferation of inedible filamentous cyanobacteria released from light and nutrient limitation after they were entrained from below the thermocline into the surface water. Thus, thermocline deepening by a single severe storm can induce prolonged responses of lake ecosystem metabolism independent of other storm-induced effects, such as inputs of terrestrial materials by increased catchment run-off. This highlights that future shifts in frequency, severity or timing of storms are an important component of climate change, whose impacts on lake thermal structure will superimpose upon climate trends to influence algal dynamics and organic matter cycling in clear-water lakes. Keywords: climate variability, ecosystem productivity, extreme events, gross primary production, mesocosm, respiration stratified lakes
KW  - climate variability
KW  - ecosystem productivity
KW  - extreme events
KW  - gross primary production
KW  - mesocosm
KW  - respiration stratified lakes
Y1  - 2017
U6  - https://doi.org/10.1111/gcb.13512
SN  - 1354-1013
SN  - 1365-2486
VL  - 23
SP  - 1448
EP  - 1462
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Weyhenmeyer, Gesa A.
A1  - Mackay, Murray
A1  - Stockwell, Jason D.
A1  - Thiery, Wim
A1  - Grossart, Hans-Peter
A1  - Augusto-Silva, Petala B.
A1  - Baulch, Helen M.
A1  - de Eyto, Elvira
A1  - Hejzlar, Josef
A1  - Kangur, Kuelli
A1  - Kirillin, Georgiy
A1  - Pierson, Don C.
A1  - Rusak, James A.
A1  - Sadro, Steven
A1  - Woolway, R. Iestyn
T1  - Citizen science shows systematic changes in the temperature difference between air and inland waters with global warming
JF  - Scientific reports
N2  - Citizen science projects have a long history in ecological studies. The research usefulness of such projects is dependent on applying simple and standardized methods. Here, we conducted a citizen science project that involved more than 3500 Swedish high school students to examine the temperature difference between surface water and the overlying air (T-w-T-a) as a proxy for sensible heat flux (Q(H)). If Q(H) is directed upward, corresponding to positive T-w-T-a, it can enhance CO2 and CH4 emissions from inland waters, thereby contributing to increased greenhouse gas concentrations in the atmosphere. The students found mostly negative T-w-T-a across small ponds, lakes, streams/rivers and the sea shore (i.e. downward Q(H)), with T-w-T-a becoming increasingly negative with increasing T-a. Further examination of T-w-T-a using high-frequency temperature data from inland waters across the globe confirmed that T-w-T-a is linearly related to T-a. Using the longest available high-frequency temperature time series from Lake Erken, Sweden, we found a rapid increase in the occasions of negative T-w-T-a with increasing annual mean T-a since 1989. From these results, we can expect that ongoing and projected global warming will result in increasingly negative T-w-T-a, thereby reducing CO2 and CH4 transfer velocities from inland waters into the atmosphere.
Y1  - 2017
U6  - https://doi.org/10.1038/srep43890
SN  - 2045-2322
VL  - 7
PB  - Nature Publ. Group
CY  - London
ER  -