Physical Factors Control Phytoplankton Production and Nitrogen Fixation in Eight Texas Reservoirs

Forbes, Margaret G.; Doyle, Robert D.; Scott, J. Thad; Stanley, Jacob K.; Huang, Hui; Brooks, Bryan W.

doi:10.1007/s10021-008-9188-2

Cited by 31 publications

(26 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Furthermore, at shallow, upreservoir sites, production rates were more strongly related to trophic state than in open-water portions of the reservoirs. A previous analysis of the 2006 data from these reservoirs demonstrated that phytoplankton production rates were related to nutrient concentrations only at shallow sites (Forbes et al 2008), suggesting a hierarchical structure in predictor variables at spatial scales . del Giorgio and Peters (1993) found that mean planktonic production (mg C m -3 day -1 ) was positively correlated with trophic state (as inferred by chlorophyll concentrations, Eq.…”

Section: Discussionmentioning

confidence: 85%

“…The reservoirs are likely monomictic, although occasional polymixis may occur. Portions of the study have been published elsewhere: maximum planktonic production and nitrogen fixation rates, nutrient data, and watershed analysis appear in Forbes et al (2008). Four reservoirs (Aquilla, Conroe, Lewisville, and Cedar Creek) were sampled twice, once in summer 2005 and again in summer 2006; four additional reservoirs (Buchanan, Canyon, Stillhouse Hollow, and Texana) were sampled once in summer 2006.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Carbon sink to source: longitudinal gradients of planktonic P:R ratios in subtropical reservoirs

et al. 2010

Self Cite

View full text Add to dashboard Cite

Spatial patterns of planktonic production and respiration in the surface mixed layer were examined in eight Texas, USA reservoirs to test the hypothesis that P:R ratios are lowest in upreservoir inflow zones and highest in downreservoir open-water zones, as predicted by the heuristic reservoir zonation model. We measured summer planktonic metabolism with light-dark bottles and physical-chemical conditions in epilimnetic water at 85 sites distributed among sixteen longitudinal transects within the eight reservoirs (2 transects per reservoir). Volumetric production and plankton biomass were lowest in the open-water zones and increased upreservoir; however, that pattern was reversed for areal production due to greater photic depths at open-water sites. Volumetric respiration was similar in the three zones; however, corresponding planktonic P:R ratios in the surface mixed layer were significantly lower at open-water sites, which is opposite than hypothesized. Based on linear regressions of production and respiration rates on chlorophyll a, open-water sites were net heterotrophic during the summer regardless of trophic state; whereas inflow and mid-reservoir zone sites were heterotrophic when chlorophyll concentrations were respectively less than 9.5 and 35 mg m -3 . Although variation among reservoirs was high, five of the eight reservoirs had inflow zones that were net carbon sinks while seven had open-water zones that were carbon sources. Mean (±standard error) carbon flux rates of inflow, midreservoir, and open-water zones were -0.22 ± 0.12 (C sink), 0.39 ± 0.44 (moderate C source), and 1.33 ± 0.50 (strong C source) g C m -2 day -1 respectively. Inflow and mid-reservoir zones comprised approximately 45% of the total reservoir area studied. Therefore, omitting their contribution as often done when a single open-water site is sampled may substantially overestimate reservoir carbon flux.

show abstract

Section: Discussionmentioning

confidence: 85%

Section: Methodsmentioning

confidence: 99%

Carbon sink to source: longitudinal gradients of planktonic P:R ratios in subtropical reservoirs

et al. 2010

Self Cite

View full text Add to dashboard Cite

show abstract

“…Maximum volumetric rates increased in August and September 2004 but were never more than 50% of the rates observed in 2003. Forbes et al (2008) compared summer N 2 fixation rates in main bodies and arms of 8 Texas reservoirs and found that volumetric N 2 fixation rates were highest in systems with small relative drainage areas. While the precise mechanisms have not been determined, these systems presumably had longer detention times, more frequent periods of stagnation, and reduced hydraulic flushing.…”

Section: Interannual Variabilitymentioning

confidence: 99%

“…More recently, Arhonditsis et al (2007) found that along a riverine-to-estuarine gradient, cyanobacteria favored downstream conditions where hydrologic forcing was reduced. Forbes et al (2008) demonstrated that, at various locations within warm, polymictic reservoirs, higher rates of nitrogen fixation occurred at sites with smaller drainage area to water surface area ratios and presumably lower flushing potential. Patoine et al (2006) found that in a series of northern United States lakes, both areal and volumetric estimates of N 2 fixation were strongly correlated to drainage area and lake position along a longitudinal gradient.…”

mentioning

confidence: 99%

“…These conditions may be common in southern reservoirs during summer periods with reduced river inflows. Scott et al (2008) and Forbes et al (2008) have recently demonstrated the hierarchical nature of key environmental factors regulating nitrogen fixation, including water temperature, nutrient concentrations, relative watershed size, seasonal hydrologic regime, and nutrient loading.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Hot spots and hot moments of planktonic nitrogen fixation in a eutrophic southern reservoir

Doyle

Scott

Forbes

2010

Lake and Reservoir Management

Self Cite

View full text Add to dashboard Cite

Environmental factors and thresholds for nitrogen fixation by phytoplankton in tropical reservoirs

Moutinho

Marafão

Calijuri

et al. 2020

Internat Rev Hydrobiol

View full text Add to dashboard Cite

In theory, the phytoplankton community of freshwater ecosystems with low concentrations of dissolved inorganic nitrogen (DIN) can obtain this element by atmospheric nitrogen (N2) fixation. This process could explain the dominance of cyanobacteria in tropical reservoirs, yet is rarely quantified in these systems. Assessing the factors related to N2fixation can assist in the management of cyanobacterial blooms. Our study characterized environmental factors related to N2fixation in Brazilian tropical reservoirs with contrasting trophic states, and defined quantitative thresholds for water chemistry and physical characteristics that stimulated N2fixation. We used field assays with15N for estimating N2fixation rates by phytoplankton. The highest rates normalized by chlorophyll‐a(maximum of 143 × 10−4 μg‐N μg‐Chl‐a−1 h−1) coincided with eutrophic conditions and presence of diazotrophs. Receiver operating characteristic (ROC) analysis provided significant thresholds for water temperature (≥22°C), soluble reactive phosphorus (SRP) (≥3.0 μg‐P L−1), total phosphorus (TP) (≥20.5 μg‐P L−1), DIN:SRP (≤487) and DIN:TP (≤82) molar ratios, chlorophyll‐a(≥12 μg L−1), and total suspended solids (≥4 mg L−1). Censored regressions confirmed that temperature, chlorophyll‐a, and phosphorus were important predictors of N2fixation rates. In general, the N2fixation rates determined in this study were lower than those found for temperate reservoirs. However, the temperature threshold of 22°C or above, identified in our analysis, suggests that phytoplankton have the potential to fix N2throughout the year in tropical reservoirs. Our results suggested that phosphorus is the main nutrient controlling the rates of N2fixation when N2‐fixing cyanobacteria were present. Phosphorus abatement is, thus, crucial for managing the trophic state and controlling N2‐fixing cyanobacteria in these ecosystems.

show abstract

Physical Factors Control Phytoplankton Production and Nitrogen Fixation in Eight Texas Reservoirs

Cited by 31 publications

References 46 publications

Carbon sink to source: longitudinal gradients of planktonic P:R ratios in subtropical reservoirs

Carbon sink to source: longitudinal gradients of planktonic P:R ratios in subtropical reservoirs

Hot spots and hot moments of planktonic nitrogen fixation in a eutrophic southern reservoir

Environmental factors and thresholds for nitrogen fixation by phytoplankton in tropical reservoirs

Contact Info

Product

Resources

About