Epilithic nitrogen fixation in the rocky littoral zones of Lake Malawi, Africa

Higgins, Scott N.; Hecky, Robert E.; Taylor, William D.

doi:10.4319/lo.2001.46.4.0976

Cited by 28 publications

(18 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The highest substrate-scaled N 2 -fixation rate observed in any of our lakes or streams was approximately 1,000 lg N m -2 h -1 ; peak rates for epiphytes in the lake and on rocks in streams were more frequently around 200-300 lg N m -2 h -1 . These rates were quite similar to benthic rates observed on rock substrates in tropical and subalpine oligotrophic lakes (Loeb and Reuter 1981;Higgins et al 2001) and by epiphytes in a tropical lake (Doyle and Fisher 1994). The lack of pelagic N 2 fixation was expected and has been observed in other oligotrophic lakes (Mague and Burris 1973;Flett et al 1980;Reuter and Axler 1992).…”

Section: Discussionsupporting

confidence: 76%

Nitrogen fixation varies spatially and seasonally in linked stream-lake ecosystems

Marcarelli

Wurtsbaugh

2009

Biogeochemistry

View full text Add to dashboard Cite

We performed surveys of nitrogen (N 2 )-fixation in three oligotrophic lake-stream systems in the Sawtooth Mountains of central Idaho to address two questions: (1) Which habitat types within linked lake-stream systems (lake pelagic, lake benthic, and stream) exhibit the highest rates of N 2 fixation?, and (2) How does N 2 fixation compare to the hydrologic flux of nitrogen? A seasonal survey showed that N 2 fixation in a single lake and its outlet stream peaked in late summer, when hydrologic N fluxes were lowest. Benthic lake N 2 -fixation rates by epiphytes were highest at mid-lake depths, where their percent cover was highest, while rates by epipelon were greatest at shallow lake depths. Pelagic N 2 fixation was below detection. Stream N 2 -fixation rates were greatest on rock substrates and in the lake outlet stream. These patterns were supported by a baseflow survey (late July) in three lake-stream ecosystems which confirmed that N 2 -fixation rates peaked in the lake benthos at shallow depths and on rock substrates in outlet streams. Scaling N 2 -fixation rates to whole lake and stream areas revealed that N 2 fixation could exceed the nitrate, and sometimes the total dissolved nitrogen flux during baseflow in lakes and outlet streams. Despite low rates, total N 2 -fixation contributions (kg/day) from lakes were greater because they had far larger surface areas than the stream environments. Fixed nitrogen contributions from stream outlets were also relatively high because of high N 2 -fixation rates and despite low surface areas. This study suggests that N 2 fixation could be a seasonally important nitrogen source to nutrient deficient subalpine lake-stream ecosystems. In addition, the frequency and location of lakes could control N 2 -fixation contributions to watersheds by providing a large area for within-lake N 2 fixation, and creating conditions favorable for N 2 fixation in outlet streams.

show abstract

Section: Discussionsupporting

confidence: 76%

Nitrogen fixation varies spatially and seasonally in linked stream-lake ecosystems

Marcarelli

Wurtsbaugh

2009

Biogeochemistry

View full text Add to dashboard Cite

show abstract

“…We may have underestimated PO 4 3-turnover by not accounting for roughness of the substratum, which greatly increases its actual surface area (e.g. Higgins et al, 2001) and the uptake contributed by the abundant macrophytes and their epiphytes. While it is premature to speculate on the relative importance of other substrata to the dynamics of the system, these are areas that deserve further study.…”

Section: Discussionmentioning

confidence: 99%

Phosphate uptake by seston and epilithon in the Grand River, southern Ontario

2006

Self Cite

View full text Add to dashboard Cite

Phosphate uptake and release by epilithon and seston were measured in the eutrophic Grand River during May to October over three years. Measurements were performed in stirred beakers of freshly collected river water containing seston and, for measurements of uptake by epilithon, unglazed ceramic tiles that had been colonized by epilithon in the river. Areal PO 4 3-uptake was dominated by the epilithon, especially when the water level was low, although uptake per ash-free dry mass was greater for seston. Uptake rates varied on both short (<1 day) and longer (week to week) time scales. Uptake was suffi cient to turn over the dissolved PO 4 3-pool in as little as 27 min when soluble reactive phosphorus (SRP) concentration was low, but the average turnover time was >1 h. On average, about half of sestonic PO 4 3-uptake was by the picoplankton (0.2-2.0 µm) size-fraction, and this fraction was most important when total uptake was low. Net changes in SRP during incubations of river water were consistent with both epilithon and seston regenerating PO 4 3-, at least at times, so that net uptake is less than gross uptake and probably near zero at low fl ow. These net uptake experiments also served to highlight some diffi culties with measuring P dynamics in microcosms, especially that uptake and regeneration are high enough that PO 4 3-, and therefore PO 4 3-uptake, can change rapidly in microcosms fi lled with river water.

show abstract

“…The vacutainers were kept in the dark at low temperature (4°C) in the fridge until analyzed. N 2 -fixation rates (lg N m À3 h À1 ) at each irradiance level were estimated from ethylene production from acetylene assuming a conversion factor of 3 moles of ethylene produced per mole of N 2 -fixed (Hardy et al, 1968;Higgins et al, 2001). The final N 2 -fixation rates were corrected using appropriate dilution factors to reflect natural densities of heterocystous Anabaena filaments in the lake.…”

Section: Water Samplingmentioning

confidence: 99%

“…Despite its importance to the lake's N budget, measurements of planktonic N 2 -fixation are very few (Guildford et al, 1999). In contrast rates of epilithic N 2 -fixation in the lake are well characterized and are among the highest rates in freshwater and marine ecosystems of the world (Higgins, 1999;Higgins et al, 2001).…”

Section: Introductionmentioning

confidence: 99%