A retrospective analysis of nutrients and phytoplankton productivity in the Mississippi River plume

Lohrenz, Steven E.; Redalje, Donald G.; Cai, Wei‐Jun; Acker, James G.; Dagg, M.

doi:10.1016/j.csr.2007.06.019

Cited by 112 publications

(78 citation statements)

References 52 publications

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“…While this biogeochemical model is capable of simulating phosphate and the inorganic carbon processes in addition to nitrogen cycling, we focused on the nitrogen cycle first in this work. Omission of phosphate cycling is justified by results of earlier studies (e.g., Rabalais et al, 2002) that have shown that the primary production on the LATEX shelf is typically nitrogen-limited during the low discharge season, and that dissolved NO x : PO 4 ratios are often higher than the 16 : 1 "Redfield ratio" (Lohrenz et al, 2008;Lohrenz et al, 1997;Lohrenz et al, 1999). An understanding of the role of phosphate and how its rapid recycling affects regional marine ecosystem processes warrants more detailed study (e.g., Laurent et al, 2012 for the LATEX shelf).…”

Section: Biogeochemical Modelmentioning

confidence: 99%

“…We also took advantage of extensive in situ observations (shipboard CTD casts and Niskin bottle samplings) collected during research cruises in the northern GoM spanning over the period of 2005-2010 (Data were collected from different sources, including the Environmental Protection Agency; Lehrter et al, 2009Lehrter et al, , 2012Lohrenz et al, 2008;Cai et al, 2011;Huang et al, 2012; Louisiana Universities Marine Consortium; Rabalais et al, 2007; Mechanisms Controlling Hypoxia (MCH) Project; Southeast Monitoring and Assessment Program (SEAMAP); the NSF-funded GulfCarbon Project and Mississippi-Atchafalaya-Gulf of Mexico Mixing Experiment (MMAGMIX)). Together, there are more than 8000 surface observations of water temperature, salin- ity, NO 3 , NH 4 , and chlorophyll concentrations.…”

Section: Model-data Comparisonsmentioning

confidence: 99%

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Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico

Xue

Fennel

et al. 2013

Biogeosciences

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Abstract.A three-dimensional coupled physicalbiogeochemical model is applied to simulate and examine temporal and spatial variability of circulation and biogeochemical cycling in the Gulf of Mexico (GoM). The model is driven by realistic atmospheric forcing, open boundary conditions from a data assimilative global ocean circulation model, and observed freshwater and terrestrial nitrogen input from major rivers. A 7 yr model hindcast (2004)(2005)(2006)(2007)(2008)(2009)(2010) was performed, and validated against satellite observed sea surface height, surface chlorophyll, and in situ observations including coastal sea level, ocean temperature, salinity, and dissolved inorganic nitrogen (DIN) concentration. The model hindcast revealed clear seasonality in DIN, phytoplankton and zooplankton distributions in the GoM. An empirical orthogonal function analysis indicated a phaselocked pattern among DIN, phytoplankton and zooplankton concentrations. The GoM shelf nitrogen budget was also quantified, revealing that on an annual basis the DIN input is largely balanced by the removal through denitrification (an equivalent of ∼ 80 % of DIN input) and offshore exports to the deep ocean (an equivalent of ∼ 17 % of DIN input).

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Section: Biogeochemical Modelmentioning

confidence: 99%

Section: Model-data Comparisonsmentioning

confidence: 99%

Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico

Xue

Fennel

et al. 2013

Biogeosciences

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“…Continental margin waters that receive input from large rivers are characterized by high biological productivity, intense biogeochemical cycling, and strong ecological gradients in environmental conditions and phytoplankton abundance and community composition (Smith & Demaster 1996, Lohrenz et al 2008, Zhou et al 2008, Goes et al 2014. The northern Gulf of Mexico (NGOM) is an example of such a large river system, strongly influenced by the Mississippi− Atchafalaya river system (the third largest river basin of the world, covering over 3.2 × 10 6 km 2 , draining > 80% of the continental USA; after Dunn 1996).…”

Section: Introductionmentioning

confidence: 99%

Phytoplankton community structure in the river‑influenced continental margin of the northern Gulf of Mexico

Chakraborty¹,

Lohrenz

2015

Mar. Ecol. Prog. Ser.

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Phytoplankton community composition was characterized over varying seasonal and river discharge conditions during 5 research cruises across the continental margin of the northern Gulf of Mexico (NGOM). The spatial and temporal patterns of variation in the composition of the algal community were examined using high performance liquid chromatography (HPLC) analyses of phytoplankton pigments in conjunction with classification using the CHEMTAX software (v.1.95). Cluster analysis and principal component analysis were used to identify different regimes and to understand the relationship of the phytoplankton community to biological and environmental variables. The large river dominated margin of the NGOM was characterized by (1) an estuarine and inner shelf regime dominated by diatoms, cryptophytes, cyanobacteria, and chlorophytes; (2) midshelf waters, a transition zone between coastal river-influenced and oligotrophic slope waters, associated with a mixed phytoplankton composition; and (3) a slope water regime typical of oligotrophic ocean conditions with a surface community dominated by cyanobacteria, haptophytes, and prochlorophytes. A chlorophyll fluorescence maximum (CFM) was a regular feature at offshore stations and showed significant differences from that of surface waters in seasonal variability of phytoplankton pigment ratios and community composition. Our findings support the view that large river outflows, along with other environmental variables such as wind forcing and stratification, have a profound influence on phytoplankton communities over a large regional extent in the continental margin waters of the NGOM.

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“…This is a considerable effect that apparently has played a role also in the past, as reflected by the coinciding historical increases in r and decreases in [DIN] observed in the lower parts of the Amy Darya River (Törnqvist et al 2015). Without further investigation, one cannot exclude the possibility that similar effects of enhanced retention-attenuation can have contributed to decreasing [DIN] trends observed in several rivers of irrigated basins across the world, despite unchanged or increased fertilizer use (e.g., Bouraoui and Grizzetti 2011;Lohrenz et al 2008), in contrast to the global average trends of increasing [DIN] (Seitzinger et al 2010). Regarding future conditions in Central Asia, climate projections (Lioubimtseva and Henebry 2009; Koirala et al 2014) suggest that temperatures will increase and runoff decrease in a similar way as in the ASDB, which implies that also other Central Asian rivers may be subject to similar changes in retention-attenuation of DIN as the here investigated principal Amu Darya River.…”

Section: Changing Regional Climatementioning

confidence: 97%

Climate-driven change of nitrogen retention–attenuation near irrigated fields: multi-model projections for Central Asia

Jarsjö

Törnqvist

2017

Environ Earth Sci

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Agricultural intensification in semiarid regions comes at a cost of relatively high water losses through evapotranspiration and can contribute to releases of nutrients and pesticides that affect downstream water quality. In addition, highly managed river basins may be particularly sensitive to future climate change. However, effects on retention-attenuation of nutrients are difficult to quantify due to the complexity and variability of relevant processes. We here use the example case of the large (covering 1.3% of the earth's land surface) and extensively irrigated Aral Sea Drainage Basin (ASDB) in Central Asia, together with 73 general circulation model (GCM) projection results and field-data driven nitrogen retention-attenuation modeling, to investigate to which extent projected future climate change (for years 2025, 2050 and 2100) can influence nitrogen loads and concentrations in the water systems of the basin. Results for the principal Amu Darya River of the ASDB suggest that riverine concentrations of nitrogen will decrease considerably throughout the coming century. This is due to projected climate-related decreases in runoff and river discharge, which increases internal nitrogen recirculation ratios, average transport distances and nitrogen retention-attenuation. However, in groundwater near the agricultural fields, there is in contrast a risk of considerable nitrogen accumulation. More generally, the sensitivity of nitrogen concentrations in the ADRB to climate-driven changes in runoff and discharge is likely to be shared with many highly managed basins in arid and semiarid regions of Central Asia, and the world.

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A retrospective analysis of nutrients and phytoplankton productivity in the Mississippi River plume

Cited by 112 publications

References 52 publications

Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico

Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico

Phytoplankton community structure in the river‑influenced continental margin of the northern Gulf of Mexico

Climate-driven change of nitrogen retention–attenuation near irrigated fields: multi-model projections for Central Asia

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