Pelagic Nitrogen Fixation in Lake Victoria (East Africa)

Mugidde, R.; Hecky, Robert E.; Hendzel, L. L.; Taylor, William D.

doi:10.1016/s0380-1330(03)70540-1

Cited by 89 publications

(108 citation statements)

References 34 publications

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“…Some studies have indicated that N-fixing cyanobacteria become dominant in summer with a nitrogen shortage (Mugidde et al 2003;Marcarelli and Wurtsbaugh 2009;Paterson et al 2011). However, N-fixing cyanobacteria did not dominate the phytoplankton community in several additional studies under analogous circumstances (Havens et al 2003;Scott and McCarthy 2010;Gikuma-Njuru et al 2013).…”

Section: Discussionmentioning

confidence: 99%

Differences in phytoplankton dynamics and community structure between a wet year and dry year in the Zhoucun Reservoir

Qiu

Zeng

2016

Journal of Freshwater Ecology

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Rainfall-induced nutrient fluctuations in surface water affect phytoplankton communities and cause algal blooms. To examine this influence in the Zhoucun Reservoir, China, field surveys were performed weekly or biweekly from February 2013 (a wet year) to December 2014 (a dry year). Physical conditions, nutrient levels, and phytoplankton functional groups were investigated during monitoring. Nutrient levels increased in the summer of 2013 (TN: 0.85À2.66 mg/L; TP: 0.037À0.138 mg/L), while nitrogen deficiency occurred in the summer of 2014 (TN: 0.38À0.73 mg/L, TP: 0.044À0.079 mg/L). A cyanobacteria bloom that appeared in the summer of 2013 had the dominant phytoplankton functional groups M and Tc. In the summer of 2014, algal cell density and biomass were much lower than those during the corresponding period in 2013, and the co-dominant phytoplankton groups were F, L 0 , Tc, and S2. Non-N-fixing cyanobacteria were not abundant in summer 2013 probably because of the low ratio of NO 3 ¡ to NH 4 C , although nitrogen was also deficient. In contrast to these summer trends, little difference was noted between phytoplankton dynamics and community structure in the two winters and two springs, regardless of nutrient conditions. Redundancy analysis indicated that rainfall-induced nitrogen fluctuations were the primary factor causing phytoplankton dynamics to differ between the wet and dry year. The effects of water temperature, stratification, and light on the phytoplankton community were independent of nutrient fluctuations. This study shows that rainfall fluctuations change summer nutrient conditions and that cyanobacteria blooms are likely to occur in wet years in the Zhoucun Reservoir.

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Section: Discussionmentioning

confidence: 99%

Differences in phytoplankton dynamics and community structure between a wet year and dry year in the Zhoucun Reservoir

Qiu

Zeng

2016

Journal of Freshwater Ecology

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“…The positive slope of deg is in the opposite direction of the slope of POM so variation in deg isotopes can only be explained by a shift to isotopically heavier prey as both d13C and d15 N increase together from earlier to later years. The species pyr and lap did not extend their habitat to deeper water (as would be expected from the POM data and from the lighter d 13 C signatures in these species through the 1980s and 1990s) but rather they occupied shallower collected from inshore and offshore stations along a transect from Mwanza in the south to Port Bell in the north of Lake Victoria in October 1995 and from location V96-5MC in the middle of the lake, from Bugaia Island in the northern part of the lake and from several offshore sites in 1995/1996 (see Campbell et al, 2003a;Mugidde et al, 2003;Hecky et al, 2010) water (Seehausen et al, 1997b;Kishe-Machumu et al, 2015). However, stomach and gut content analysis revealed a higher intake of chironomids, detritus and molluscs during the late 1980s and 1990s of both species (Katunzi et al, 2003;Kishe-Machumu 2012;van Rijssel et al, 2015), indicating a more benthic feeding behaviour during this period.…”

Section: Geographical Variationmentioning

confidence: 97%

“…Every 20 km, surface water samples were taken from the trans-lake ferry MV Bukoba in October 1995. Additionally, water samples were taken from location V96-5MC in the middle of the lake, from Bugaia Island in the northern part of the lake in July 1995 and April 1996 (Campbell et al, 2003a;Hecky et al, 2010) and from offshore sites XL1, XL4, XL6-9 in May 1995 (Mugidde et al, 2003). Stable isotope signatures were derived from these samples using the methods of Hecky & Hesslein (1995) at the Freshwater Institute Laboratory (Winnipeg, Canada) and were also Suess corrected (Verburg, 2007).…”

Section: Stable Isotope Analysismentioning

confidence: 99%

“…The eutrophication is thought to be caused by agricultural malpractices, urbanization and deforestation, although recent studies have suggested that climatic variability and wind stress played a crucial role as well (Kolding et al, 2008;Hecky et al, 2010;van Rijssel, 2014). Most of the studies reporting eutrophication focussed on the northern part of the lake (Hecky, 1993;Mugidde, 1993;Mugidde et al, 2003) and because of the lack of regular and consistent measurements of biological productivity, paleolimnological analysis was used to provide more continuous analysis of historical changes in the ecosystem.…”

Section: Introductionmentioning

confidence: 99%

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Changing ecology of Lake Victoria cichlids and their environment: evidence from C13 and N15 analyses

et al. 2016

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Eutrophication is an increasing global threat to freshwater ecosystems. East Africa's Lake Victoria has suffered from severe eutrophication in the past decades which is partly responsible for the dramatic decline in haplochromine cichlid species diversity. However, some zooplanktivorous and detritivorous haplochromine species recovered and shifted their diet towards macro invertebrates and fish. We used four formalin preserved cichlid species caught over the past 35 years to investigate whether stable isotopes of these fish are reflecting the dietary changes, habitat differences and if these isotopes can be used as indicators of eutrophication. We found that d 15 N signatures mainly reflected dietary shifts to larger prey in all four haplochromine species. Shifts in d 13 C signatures likely represented habitat differences and dietary changes. In addition, a shift to remarkably heavy d 13 C signatures in 2011 was found for all four species which might infer increased primary production and thus eutrophication although more research is needed to confirm this hypothesis. The observed temporal changes confirm previous findings that preserved specimens can be used to trace historical changes in fish ecology and the aquatic environment. This highlights the need for continued sampling as this information could be of essence for reconstructing and predicting the effects of environmental changes.

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“…During the past two decades, culture-independent amplification of the nifH gene has been successfully applied to examine the diversity and related functions of N-fixing microorganisms in various habitats (e.g., Zehr et al 1995Zehr et al , 1997Zehr et al , 2003Shaffer et al 2000;Affourtit et al 2001). It is well known that planktonic N fixation in eutrophic lakes is one of the most important biological mechanisms for converting N 2 to combined N (Torrey and Lee 1976;Howarth et al 1988a;Mugidde et al 2003). Surprisingly, there has been no previous research on N 2 fixation and its contribution to the ecosystem of the largest urban lake in China (Lake Donghu), although systematic ecological studies have been conducted in the lake during the previous decades (e.g., Liu 1995).…”

Section: Introductionmentioning

confidence: 99%

Diversity of nifH gene amplified from plankton-community DNA in a shallow eutrophic lake (Lake Donghu, Wuhan, China)

Yan

Feng

2010

Limnology

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Biological nitrogen fixation (BNF) is one of the major nitrogen inputs into the biosphere, and the nitrogenase iron protein (nifH) gene plays important roles in regulating the molecular nitrogen (N 2 ) fixation process. The nifH gene has also been extensively used to study the diversity and function of nitrogen-fixing microorganisms. In this study, we investigated the diversity of the nifH gene by culture-independent methods to analysis the planktonic nitrogen-fixing organisms in Lake Donghu, Wuhan, the largest urban lake in China. Results indicate that nifH gene sequences cloned from planktonic-community DNA showed high similarity to the uncultured cyanobacterial sequences deposited in the GenBank database. Phylogenetic analysis on the basis of the translated amino acid sequences further showed that most nifH clones were closely related to the reported cyanobacterial nifH gene sequences. Results also indicate that there are similar planktonic nitrogen-fixing organisms in the relatively independent areas of Lake Donghu, even though different regions showed a wide gradient in trophic status. These and other observations led us to believe that studies on nifH gene diversity and expression will increase our ability to understand the ecological function of target nitrogen-fixing groups in aquatic ecosystems.

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Pelagic Nitrogen Fixation in Lake Victoria (East Africa)

Cited by 89 publications

References 34 publications

Differences in phytoplankton dynamics and community structure between a wet year and dry year in the Zhoucun Reservoir

Differences in phytoplankton dynamics and community structure between a wet year and dry year in the Zhoucun Reservoir

Changing ecology of Lake Victoria cichlids and their environment: evidence from C13 and N15 analyses

Diversity of nifH gene amplified from plankton-community DNA in a shallow eutrophic lake (Lake Donghu, Wuhan, China)

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