The concept of microbial affinity for limiting nutrients in steady state and rhythmic systems

Thesis (Ph.D.) University of Alaska Fairbanks, 198

The regional and global significance of nitrogen removal in lakes and reservoirs

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 93 (2009): 143-157, doi:10.1007/s10533-008-9272-x.Human activities have greatly increased the transport of biologically available N through watersheds to potentially sensitive coastal ecosystems. Lentic water bodies (lakes and reservoirs) have the potential to act as important sinks for this reactive N as it is transported across the landscape because they offer ideal conditions for N burial in sediments or permanent loss via denitrification. However, the patterns and controls on lentic N removal have not been explored in great detail at large regional to global scales. In this paper we describe, evaluate, and apply a new, spatially explicit, annual-scale, global model of lentic N removal called NiRReLa (Nitrogen Retention in Reservoirs and Lakes). The NiRReLa model incorporates small lakes and reservoirs than have been included in previous global analyses, and also allows for separate treatment and analysis of reservoirs and natural lakes. Model runs for the mid-1990s indicate that lentic systems are indeed important sinks for N and are conservatively estimated to remove 19.7 Tg N yr-1 from watersheds globally. Small lakes (< 50 km2) were critical in the analysis, retaining almost half (9.3 Tg N yr-1) of the global total. In model runs, capacity of lakes and reservoirs to remove watershed N varied substantially (0-100%) both as a function of climate and the density of lentic systems. Although reservoirs occupy just 6% of the global lentic surface area, we estimate they retain approximately 33% of the total N removed by lentic systems, due to a combination of higher drainage ratios (catchment surface area : lake or reservoir surface area), higher apparent settling velocities for N, and greater N loading rates in reservoirs than in lakes. Finally, a sensitivity analysis of NiRReLa suggests that, on-average, N removal within lentic systems will respond more strongly to changes in land use and N loading than to changes in climate at the global scale.The NSF26 Research Coordination Network on denitrification for support for collaboration (award number DEB0443439 to S.P. Seitzinger and E.A. Davidson). This project was also supported by grants to J.A. Harrison from California Sea Grant (award number RSF8) and from the U.S. Geological Survey 104b program and R. Maranger (FQRNT Strategic Professor)

The effectiveness of cyanobacteria nitrogen fixation: Review of bench top and pilot scale nitrogen removal studies and implications for nitrogen removal programs

One of the primary goals of eutrophication management of freshwater systems is to lower the risk of cyanobacterial blooms. This is typically accomplished at the watershed scale by placing controls on phosphorus (P) discharge from point sources. However, several researchers have questioned the predominance of the P management paradigm, arguing that dual nitrogen (N) and P controls would be more effective at preventing cyanobacteria blooms than P controls alone. This hypothesis is predicated in part on the hypothesis that if cyanobacteria are starved of N, which is an essential nutrient, cyanobacteria N2 fixation rates will not be high enough to maintain growth rates and biomass yields at or near previous levels. However, several single species cultures of heterocystous cyanobacteria directly examining the effect of removing N show that, when deprived of ammonium and nitrate, N2 fixing cyanobacteria compensate biochemically for the high energy cost of fixation when supplied with sufficient nutrients other than N. Biomass and growth rates were only slightly different under N2 than when grown under ammonium and nitrate, which is consistent with observations from the long-term experimental fertilization of Lake 227. Collectively, these bench top and pilot scale studies suggest that N control programs will not have a major impact on the magnitude of freshwater cyanobacteria blooms, although cyanobacteria species composition and toxin production might be affected.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Initial composition of filtered sample.

<p>Aluminum and iron were determined by ICP-MS (Thermo X II ICPMS). Other analytical methods are described in Ontario Ministry of the Environment [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128884#pone.0128884.ref019" target="_blank">19</a>].</p><p>Initial composition of filtered sample.</p

Spectral distribution of irradiation at intensity 700 W m^-2 inside the irradiation chamber and inside the Teflon tube.

<p>Spectral distribution of irradiation at intensity 700 W m^-2 inside the irradiation chamber and inside the Teflon tube.</p

Changes in DOC, POC, and DIC concentrations during irradiation.

<p><b>A–at 25°C; B–at 9°C.</b> Points represent measured data. Solid lines represent modeled trends.</p

Modeled initial concentrations, and individual transformation pathway rate constants at different temperatures ± standard errors.

<p>L.T.–laboratory temperature, approximately 23°C.</p><p>Modeled initial concentrations, and individual transformation pathway rate constants at different temperatures ± standard errors.</p

Changes in pH during irradiation experiments at different temperatures.

<p>Changes in pH during irradiation experiments at different temperatures.</p

Internal iron loading and warm temperatures are pre-conditions for cyanobacterial dominance in embayments along Georgian Bay, Great Lakes

Previous work suggests that a high rate of internal ferrous iron (Fe2+) loading from anoxic sediments into overlying waters favours cyanobacteria dominance (> 50% of the phytoplankton biomass) over eukaryotic algae. This Cyanobacteria-Ferrous conceptual model was assessed along the Georgian Bay coastline of Lake Huron, Ontario in one meso-eutrophic and three oligotrophic embayments which experience natural hypolimnetic anoxia. Cyanobacteria dominated all embayments in the relatively warmer summer of 2012 but not in much cooler 2014 although hypolimnetic anoxia and internal Fe2+ loading were observed in both summers in all embayments. A cyanobacteria bloom large enough to turn the lake visibly green was observed only in warmer 2012 in the meso-eutrophic embayment. Results show that warm summer temperatures and internal Fe2+ loading are necessary pre-conditions for cyanobacteria dominance while high nutrient levels are needed to form large blooms. There were no consistent patterns between dominance and total and dissolved phosphorus (P), total nitrogen, ammonium and nitrate. Internal P loading was not a necessary pre-condition for dominance. While P removal programs will decrease phytoplankton biomass in eutrophic waters, oxidized surficial sediments must be maintained throughout an aquatic system to prevent cyanobacteria dominance.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author