TY  - JOUR
A1  - Brothers, Soren M.
A1  - Hilt, Sabine
A1  - Meyer, Stephanie
A1  - Köhler, Jan
T1  - Plant community structure determines primary productivity in shallow, eutrophic lakes
JF  - Freshwater biology
N2  - Regime shifts are commonly associated with the loss of submerged macrophytes in shallow lakes; yet, the effects of this on whole-lake primary productivity remain poorly understood. This study compares the annual gross primary production (GPP) of two shallow, eutrophic lakes with different plant community structures but similar nutrient concentrations. Daily GPP rates were substantially higher in the lake containing submerged macrophytes (58623gCm(-2)year(-1)) than in the lake featuring only phytoplankton and periphyton (40823gCm(-2)year(-1); P<0.0001). Comparing lake-centre diel oxygen curves to compartmental estimates of GPP confirmed that single-site oxygen curves may provide unreliable estimates of whole-lake GPP. The discrepancy between approaches was greatest in the macrophyte-dominated lake during the summer, with a high proportion of GPP occurring in the littoral zone. Our empirical results were used to construct a simple conceptual model relating GPP to nutrient availability for these alternative ecological regimes. This model predicted that lakes featuring submerged macrophytes may commonly support higher rates of GPP than phytoplankton-dominated lakes, but only within a moderate range of nutrient availability (total phosphorus ranging from 30 to 100gL(-1)) and with mean lake depths shallower than 3 or 4m. We conclude that shallow lakes with a submerged macrophyte-epiphyton complex may frequently support a higher annual primary production than comparable lakes that contain only phytoplankton and periphyton. We thus suggest that a regime shift involving the loss of submerged macrophytes may decrease the primary productivity of many lakes, with potential consequences for the entire food webs of these ecosystems.
KW  - macrophytes
KW  - oxygen curves
KW  - periphyton
KW  - regime shift
KW  - trophic status
Y1  - 2013
U6  - https://doi.org/10.1111/fwb.12207
SN  - 0046-5070
VL  - 58
IS  - 11
SP  - 2264
EP  - 2276
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Périllon, Cécile
A1  - Pöschke, Franziska
A1  - Lewandowski, Jörg
A1  - Hupfer, Michael
A1  - Hilt, Sabine
T1  - Stimulation of epiphyton growth by lacustrine groundwater discharge to an oligo-mesotrophic hard-water lake
JF  - Freshwater Science
N2  - Periphyton is a major contributor to aquatic primary production and often competes with phytoplankton and submerged macrophytes for resources. In nutrient-limited environments, mobilization of sediment nutrients by groundwater can significantly affect periphyton (including epiphyton) development in shallow littoral zones and may affect other lake primary producers. We hypothesized that epiphyton growth in the littoral zone of temperate oligomesotrophic hard-water lakes could be stimulated by nutrient (especially P) supply via lacustrine groundwater discharge (LGD). We compared the dry mass, chlorophyll a (chl a), and nutrient content of epiphyton grown on artificial substrates at different sites in a groundwater-fed lake and in experimental chambers with and without LGD. During the spring-summer periods, epiphyton accumulated more biomass, especially algae, in littoral LGD sites and in experimental chambers with LGD compared to controls without LGD. Epiphyton chl a accumulation reached up to 46 mg chl a/m(2) after 4 wk when exposed to LGD, compared to a maximum of 23 mg chl a/m(2) at control (C) sites. In the field survey, differences in epiphyton biomass between LGD and C sites were most pronounced at the end of summer, when epilimnetic P concentrations were lowest and epiphyton C:P ratios indicated P limitation. Groundwater-borne P may have facilitated epiphyton growth on macrophytes and periphyton growth on littoral sediments. Epiphyton stored up to 35 mg P/m(2) in 4 wk (which corresponds to 13% of the total P content of the littoral waters), preventing its use by phytoplankton, and possibly contributing to the stabilization of a clear-water state. However, promotion of epiphyton growth by LGD may have contributed to an observed decline in macrophyte abundance caused by epiphyton shading and a decreased resilience of small charophytes to drag forces in shallow littoral areas of the studied lake in recent decades.
KW  - lacustrine groundwater discharge
KW  - periphyton
KW  - littoral
KW  - nutrients
KW  - benthic
KW  - macrophytes
KW  - seepage
Y1  - 2017
U6  - https://doi.org/10.1086/692832
SN  - 2161-9549
SN  - 2161-9565
VL  - 36
SP  - 555
EP  - 570
PB  - Univ. of Chicago Press
CY  - Chicago
ER  -